Particle-optical systems and arrangements and particle-optical components for such systems and arrangements

ABSTRACT

An electron-optical arrangement provides a primary beam path for a beam of primary electrons and a secondary beam path for secondary electrons. The electron-optical arrangement includes a magnet arrangement having first, second and third magnetic field regions. The first magnetic field region is traversed by the primary beam path and the secondary beam path. The second magnetic field region is arranged in the primary beam path upstream of the first magnetic field region and is not traversed by the secondary beam path. The first and second magnetic field regions deflect the primary beam path in substantially opposite directions. The third magnetic field region is arranged in the secondary beam path downstream of the first magnetic field region and is not traversed by the first beam path. The first and third magnetic field regions deflect the secondary beam path in a substantially same direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to particle-optical systems using multiplebeamlets of charged particles, such as an electron microscopy apparatusand electron lithography apparatus.

Further the invention relates to particle-optical components andarrangements which may be used in particle-optical systems usingmultiple beamlets of charged particles; the particle-optical componentsare, however, not limited in the application to systems using multiplebeamlets. Such particle-optical components may be used inparticle-optical systems using only one single beam of charged particlesor plural beams or beamlets of charged particles.

The invention may be applied to charged particles of any type, such aselectrons, positrons, myons, ions and others.

2. Brief Description of Related Art

A conventional particle-optical system is known from U.S. Pat. No.6,252,412 B1. The electron microscopy apparatus disclosed therein isused for inspecting an object, such as a semiconductor wafer. Aplurality of primary electron beams is focused in parallel to each otheron the object to form a plurality of primary electron spots thereon.Secondary electrons generated by the primary electrons and emanatingfrom respective primary electron spots are detected. For each primaryelectron beam a separate electron beam column is provided. The pluralityof separate electron beam columns is closely packed to each other. Adensity of the primary electron beam spots formed on the object islimited by a remaining foot step size of the electron beam columnsforming the electron microscopy apparatus. Thus, also the number ofprimary electron beam spots which may be found at the same time on theobject is limited in practice resulting in a limited throughput of theapparatus when inspecting semiconductor wafers of a high surface area ata high resolution.

From U.S. Pat. No. 5,892,224, US 2002/0148961 A1, US 2002/0142496 A1, US2002/0130262 A1, US 2002/0109090 A1, US 2002/0033449 A1, US 2002/0028399A1, there are known electron microscopy apparatuses using a plurality ofprimary electron beamlets focused on the surface of the object to beinspected. The beamlets are generated by a multi-aperture plate having aplurality of apertures formed therein, wherein an electron sourcegenerating a single electron beam is provided upstream of themulti-aperture plate for illuminating the apertures formed therein.Downstream of the multiple-aperture plate a plurality of electronbeamlets is formed by those electrons of the electron beam passing theapertures. The plurality of primary electron beamlets is focused on theobject by an objective lens having an aperture which is passed by allprimary electron beamlets. An array of primary electron spots is thusformed on the object. Secondary electrons emanating from each primaryelectron spot form a respective secondary electron beamlet, such thatalso a plurality of secondary electron beamlets corresponding to theplurality of primary electron beam spots is generated. The plurality ofsecondary electron beamlets pass the objective lens, and the apparatusprovides a secondary electron beam path such that each of the secondaryelectron beamlets is supplied to a respective one of a plurality ofdetector pixels of a CCD electron detector. A Wien-filter is used forseparating the secondary electron beam path from a beam path of theprimary electron beamlets.

Since one common primary electron beam path comprising the plurality ofprimary electron beamlets and one common secondary electron beam pathcomprising the plurality of secondary electron beamlets is used, onesingle electron-optical column may be employed, and the density ofprimary electron beam spots formed on the object is not limited by afoot step size of the single electron-optical column.

The number of primary electron beam spots disclosed in the embodimentsof the above mentioned documents is in the order of some ten spots.Since the number of primary electron beam spots formed at a same time onthe object limits the throughput, it would be advantageous to increasethe number of primary electron beam spots for achieving a higherthroughput. It has been found, however, that it is difficult to increasethe number of primary electron beam spots formed at a same time, or toincrease a primary electron beam spot density, employing the technologydisclosed in those documents while maintaining a desired imagingresolution of the electron microscopy apparatus.

It is therefore an object of the present invention to provideparticle-optical systems using charged-particle beamlets of an increaseddensity and allowing to manipulate the charged-particle beamlets with anincreased accuracy.

It is a further object of the present invention to provideparticle-optical components for manipulating beams and beamlets ofcharged particles with an increased accuracy.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter particle-opticalcomponents, particle-optical arrangements and particle-optical systemsaccording to the invention may use a plurality of charged-particlebeamlets and manipulate the same with an increased accuracy.

According to one embodiment of the invention there is provided aparticle-optical arrangement for forming a plurality of charged-particlebeamlets wherein the beamlets are arranged in an array pattern of a highregularity. The high regularity array pattern is formed by the beamletsat a desired location along the beam path of the beamlets. For instance,the high regularity array pattern may be formed at an image plane orintermediate image plane where the beamlets each form a respectivefocus.

The particle-optical arrangement comprises at least one charged-particlesource for generating at least one beam of charged particles. Thecharged-particle beamlets are formed by particles of the beam of chargedparticles passing through apertures formed in the multi-aperture plate.There may be one or plural further multi-aperture plates arranged in thebeam path of the beamlets wherein the beamlets pass through aperturesformed in the one or plural further multi-aperture plates.

The particle-optical arrangement may further comprise at least onefocusing lens or other particle-optical element for manipulating the atleast one beam of charged particles and/or the plurality ofcharged-particle beamlets. Such particle-optical element typicallycontributes to an optical distortion of the particle-opticalarrangement. Such distortion deteriorates an achievable accuracy formanipulating the beamlets and will prevent the formation of the desiredhigh regularity array pattern of the beamlet array at the desiredposition in the beam path of the beamlets.

The high regularity array pattern has a particle-optical correspondencewith an array pattern of the apertures formed in the at least onemulti-aperture plate. The positions of the apertures in themulti-aperture plates are now such determined that substantially thedesired high regularity array pattern of the beamlets is formeddownstream of the at least one multi-aperture plate. The array patternof the apertures in the multi-aperture plate will then have a lowerregularity as compared to the regularity of the high regularity arraypattern.

The displacement of positions of the apertures from a high regularitypattern to form a pattern of lower regularity is, however, not limitedto compensating a distortion introduced by one or the otherparticle-optical element and may be provided for any other purposes.

It is not necessary that the increase of regularity is provided for alldirections of the patterns. It may be sufficient to increase theregularity only in one particular direction, such as a directiontransversely to a movement of the object relative to an objective lensof the arrangement Further, it may be sufficient that a projection of acertain subset of the beamlets in a predetermined direction onto a planeforms the pattern having the increased regularity when compared to acorresponding regularity determined from a corresponding subset ofapertures projected in a direction which electron-optically correspondsto the predetermined direction.

The regularities of the high regularity array pattern of the beamletsand of the lower regularity pattern of the apertures may be determinedby e.g. some suitable mathematical means such as a method fordetermining a spatial correlation between the apertures and a one- ortwo-dimensional Fourier analysis applied to the positions of centers ofthe respective beamlets and of the respective apertures.

The at least one particle-optical element may comprise a focusing lens,such as an objective lens, for focusing the beamlets onto an objectpositionable in the image plane of the particle-optical arrangement

For compensating typical distortions of focusing lenses, distancesbetween adjacent apertures in the multi-aperture plate are preferablycontinuously decreasing with an increasing distance of the respectiveapertures from a center of the array pattern formed by the apertures inthe multi-aperture plate.

According to a further embodiment of the invention there is provided aparticle-optical arrangement having, similar to the arrangementillustrated above, at least one charged-particle source, and at leastone multi-aperture plate. The arrangement may further comprise at leastone particle-optical element for manipulating at least one beam ofcharged particles generated by the source, or for manipulating theplurality of charged-particle beamlets.

Such particle-optical element typically contributes to an opticalastigmatism of the particle-optical arrangement. For compensating suchastigmatism the apertures formed in the at least one multi-apertureplate comprise apertures having an elliptical shape rather than aperfectly circular shape.

The provision of the elliptical aperture shapes is, however, not limitedto compensating an astigmatism introduced by one or the otherparticle-optical element and may be provided for any other purposes.

According to one embodiment, an ellipticity of the elliptical shapes ofthe aperture preferably increases with increasing distance from a centerof the aperture pattern for compensating an astigmatism typicallyintroduced by a focusing lens.

A long axis of the elliptical shapes may be radially oriented withrespect to a center of the aperture pattern, or the long axis may beoriented under an angle to the radial direction. If the long axis isoriented under an angle with respect to the radial direction, such anglemay increase with increasing distance from the center of the aperturepattern.

According to a further embodiment of the invention there is provided aparticle-optical arrangement comprising, similar to the arrangement asillustrated above, at least one charged-particle source, and at leastone multi-aperture plate. The arrangement may further comprise at leastone particle-optical element for manipulating the at least one beam ofcharged particles generated by the source or for manipulating aplurality of charged-particle beamlets.

The particle-optical element may contribute to an optical fieldcurvature of the arrangement.

For compensating such field curvature a diameter of the apertures formedin the multi-aperture plate changes with an increasing distance from acenter of the aperture pattern. The change of diameters may be such thatthe diameter of the apertures increases or decreases with increasingdistance from the center of the aperture pattern.

The change of diameters of the apertures is, however, not limited tocompensating a field curvature introduced by one or the otherparticle-optical element and may be provided for any other purposes.

According to a further embodiment of the invention there is provided aparticle-optical component which may be advantageously used in aparticle-optical system using a plurality of charged-particle beamlets.The particle-optical component may be used in such system forcompensating a field curvature introduced by one or the otherparticle-optical element of the system, or, the particle-opticalcomponent may be used in such system for any other suitable purpose.

The particle-optical component comprises at least one multi-apertureplate having a plurality of apertures formed therein, for manipulatingparticles of a charged-particle beamlet passing therethrough. Themulti-aperture plate is formed of plural layer portions which arearranged in substantially a single plane, wherein plural apertures areformed in each of the plural layer portions. The layer portions areformed of a material which is electrically sufficiently conductive suchthat the layer portion defining a respective aperture therein may bemaintained at a predetermined electrical potential with a sufficientaccuracy depending on the desired application. Adjacent conductive layerportions are not directly connected with each other. For electricallyseparating the adjacent conductive layer portions from each other anelectrically sufficiently resistant gap may be advantageously formedbetween such adjacent conductive layer portions. The gap is sufficientlyresistant to allow for different electrical potentials being applied tothe adjacent conductive layer portions with the sufficient accuracy.

Even though the adjacent conductive layer portions are not directlyelectrically connected with each other there may be providedpredetermined resistors for connecting adjacent conductive layerportions or non-adjacent conductive layer portions with each other formaintaining the conductive layer portions at the desired electricalpotentials.

According to a preferred embodiment there are at least two ring-shapedportions provided wherein one ring-shaped portion is positioned in aninterior of the other ring-shaped portion.

A radial width of the ring-shaped conductive layer portions preferablydecreases with an increasing distance from a center of the aperturepattern formed in the multi-aperture plate.

The multi-aperture plate described herein above may be provided formanipulating charged particles of the beamlets passing throughrespective apertures formed in the multi-aperture plate. Suchmanipulation of the beamlets may be achieved by maintaining the platedefining the respective aperture at a suitable electrical potential. Themanipulation of the beamlet may thus comprise providing a focusing,defocusing and deflecting effect or any other effect and combinations ofthese effects on the beamlet. The electrical potential at which theplate defining plural apertures is maintained may generate an electricalfield extending in a direction upstream or downstream of the beamlet andaway from the multi-aperture plate. Due to the presence of the pluralapertures in the multi-aperture plate such electrical field will deviatefrom an homogeneous field which would be generated by a plate having noapertures formed therein. The deviation from the homogeneous electricalfield may have a disadvantageous effect on the desired type ofmanipulation of the beamlet by the respective aperture.

According to a further embodiment of the invention there is provided aparticle-optical component comprising a first multi-aperture plate madeof an insulating substrate and having a plurality of apertures formedtherethrough. An interior of the apertures formed in the insulatingsubstrate is covered with a conductive layer. An advantage of suchconductive layer provided in the interior of the apertures is acontribution of the layers to screening stray electric fieldsoriginating from adjacent or more distant apertures. A conductivity ofthe layer may be designed such that a sufficient screening will beachieved.

According to a simplified design rule, a total resistance across themulti-aperture plate, i.e. the resistance between the two main flatsurfaces of the multi-aperture plate is in a range of about 250 Ω to 8MΩ, a range of about 250 Ω to 4 MΩ, a range of about 4 MΩ to 8 MΩ, arange of about 250 Ω to 800 Ω, a range of about 800 Ω to 1.5 MΩ, a rangeof about 1.5 MΩ to 3 MΩ, a range of about 3 MΩ to 5 MΩ, and/or a rangeof about 5 MΩ to 8 MΩ.

A further multi-aperture plate may be provided in close contact with thefirst multi-aperture plate on one or on both sides thereof.

According to an embodiment the conductive layer also covers one or bothmain surfaces of the first multi-aperture plate. The conductive layerthen forms an integral portion of the first multi-aperture plate, andthe further multi-aperture plate, if such is provided, will be formed indirect contact with the conductive layer, accordingly.

The further multi-aperture plate is preferably made of a conductivematerial having a conductivity higher than a conductivity of theconductive layer provided in the apertures of the first multi-apertureplate.

According to a further embodiment of the invention there is provided aparticle-optical component having at least one multi-aperture plate witha plurality of apertures formed therein, wherein the multi-apertureplate is made of a conductive material such that an electricalresistance between both main flat surfaces of the first multi-apertureplate is in a range of about 250 Ω to 8 MΩ, a range of about 250 Ω to 4MΩ, a range of about 4 MΩ to 8 MΩ, a range of about 250 Ω to 800 Ω, arange of about 800 Ω to 1.5 MΩ, a range of about 1.5 MΩ to 3 MΩ, a rangeof about 3 MΩ to 5 MΩ, and/or a range of about 5 MΩ to 8 MΩ. Theconductivity of the substrate material contributes to screeningelectrical fields generated in the apertures.

A suitable material for manufacturing the substrate may be chosen from aglass material as it is used for manufacturing a multi-channel plate foran image amplifier.

According to a further embodiment of the invention there is provided aparticle-optical component having at least one multi-aperture platehaving a plurality of beam-manipulating apertures formed therein formanipulating a charged-particle beamlet passing therethrough, whereinthe plurality of beam-manipulating apertures is arranged in apredetermined array pattern.

Further, field correcting apertures are formed in the multi-apertureplate for correcting a distortion of the electrical field generated bythe multi-aperture plate. Positions of the field correcting apertures inthe array pattern of the beam-manipulating apertures and sizes andshapes of the field correcting apertures may be chosen such that theelectrical field generated by the multi-aperture plate substantiallycorresponds to a desired electrical field upstream and/or downstream ofthe multi-aperture plate.

When the particle-optical component is used in a particle-optical systemusing a plurality of charged-particle beamlets, those beamlets will passthrough the beam-manipulating apertures rather than through the fieldcorrecting apertures. This does not exclude, however, that intermediatebeamlets pass through the field correcting apertures wherein theintermediate beamlets are removed by some other means from a bundle ofcharged-particle beamlets which the system intends to use. Such meansfor removing intermediate beamlets passing through the field correctingapertures may include beam stops arranged at suitable positions acrossthe bundle of desired charged-particle beamlets. Such stop may beadvantageously formed by a further multi-aperture plate having formedtherein plural apertures which allow the desired beamlets to passtherethrough and having no apertures formed therein at positionscorresponding to beam paths of the intermediate beamlets.

It is further possible to intercept the intermediate beamlets in theparticle-optical component itself.

Herein, the stop may be advantageously formed by a bottom of anaperture-hole being not a through-hole of the plate.

When the beam-manipulating apertures are densely packed in themulti-aperture plate, the field correcting apertures have preferably asmaller size than the beam-manipulating apertures located adjacentthereto.

Further, when seen in a circumferential direction about a center of agiven beam-manipulating aperture, the field correcting apertures arelocated circumferentially in-between other beam-manipulating aperturesdirectly adjacent to the given beam-manipulating aperture.

According to a further embodiment of the invention there is provided aparticle-optical component comprising, similar to the particle-opticalcomponents illustrated herein above, at least one multi-aperture platehaving a plurality of beam-manipulating apertures formed therein. Forcompensating deviations of an electrical field generated by themulti-aperture plate from a desired electrical field, shapes of thebeam-manipulating apertures may be designed such that additional shapefeatures are added to basic shapes of the field manipulating apertures.The basic shapes are designed according to electron-optical design rulesin view of providing a desired beam-manipulating effect on the beamletpassing through the aperture. For instance, the basic shape may be acircular shape for providing an effect of a round lens, or the basicshape may be an elliptical shape for providing an effect of anastigmatic lens.

The shape features are provided as radial recessions or protrusions inthe basic shape. The shape features of a given aperture are provided ata manifold or symmetry around a circumference of the basic shape whichcorresponds to a manifold or symmetry of an arrangement of thebeam-manipulating apertures in a surroundings of the givenbeam-manipulating beam aperture.

For instance, if a given beam-manipulating aperture has four immediatelyadjacent beam-manipulating apertures as closest neighbors, the shapefeatures of the given beam-manipulating aperture will have a fourfoldsymmetry about a center of the given aperture for compensating for anon-rotational symmetric field configuration in a volume upstream ordownstream of the given beam-manipulating aperture. Such non-rotationalsymmetric field configuration is caused by the symmetry of thebeam-manipulating apertures located about the given aperture.

The closest neighbors about a given aperture may be determined by anymethod known from the art in other technical fields. According to onepossible method a very closest neighbor to the given aperture isdetermined first by identifying that aperture among all other aperturesdifferent from the given aperture as very closest neighbor which isarranged at a minimum distance from the given aperture. Thereafter, allthose apertures different from the given apertures are identified asclosest neighbors which are arranged at a distance less than about 1.2to about 1.3 times the minimum distance from the given aperture.

For determining a symmetry of the shape features it is also possible toexamine a symmetry of a larger surroundings about a given aperture, forinstance by performing a Fourier analysis on the first array patternaround the given aperture. The given aperture will then have a shapewith at least one symmetry component corresponding to a symmetry of thefirst array pattern around the given beam-manipulating aperture. Withthis method also boundary effects of apertures close to a periphery ofan aperture pattern may be taken into account where, for example, onehalf space about the given aperture may not be occupied by otherapertures.

In a multi-aperture plate having a plurality of beam-manipulatingapertures formed therein as a limited array pattern, the plate willextend beyond the pattern of beam-manipulating apertures. Thus, anelectrical field generated by a region of the plate where no aperturesare formed will be different from a field extending from a region wherethe aperture pattern is formed, resulting in an electrical field whichdeviates from a homogeneous electrical field or other desired electricalfield in particular in a region close to a periphery of the pattern. Atthe periphery, optical properties provided by the apertures to therespective beams passing therethrough may be deteriorated as compared tooptical properties provided by apertures located at a center of thepattern.

According to a further embodiment of the invention there is provided aparticle-optical arrangement comprising, similar to the arrangementsillustrated above, a multi-aperture plate having a plurality ofbeam-manipulating apertures formed therein for manipulating a pluralityof charged-particle beamlets. The beam-manipulating apertures arearranged in a first array pattern and there are field correctingapertures formed in the multi-aperture plate in a region adjacent to thefirst array pattern.

The field correcting apertures may be arranged in an array forming anextension of the array pattern of the beam-manipulating apertures.

The beamlets which the particle-optical arrangement is intended toprovide do not pass through the field correcting apertures. This doesnot exclude, however, that intermediate beamlets passing through thefield correcting apertures are intercepted by some other meansdownstream of the field correcting aperture or within the fieldcorrecting aperture as described above.

According to a further embodiment of the invention there is provided aparticle-optical arrangement comprising, similar to the arrangementsdescribed herein above, at least one charged-particle source, at leastone multi-aperture plate having a plurality of apertures formed therein,a first voltage supply for supplying predetermined first voltages to theplurality of apertures, a first single-aperture plate arranged at adistance upstream or downstream from the multi-aperture plate, and asecond voltage supply for supplying a predetermined second voltage tothe first single-aperture plate.

The apertures in the multi-aperture plate are provided for manipulatingcharged-particle beamlets passing therethrough. A manipulating effect ofthe apertures is, amongst others, determined by an electric fieldgenerated by the multi-aperture plate upstream and/or downstreamthereof. The single-aperture plate is provided upstream and downstream,respectively, to the multi-aperture plate for shaping the electricalfield to a desired shape such that the manipulating effect of theapertures is varied across the aperture pattern according to a desireddependency.

According to an embodiment, the single-aperture plate is arranged at adistance less than 75 mm from the multi-aperture plate, preferably at adistance less than 25 mm and further preferred at a distance less than10 mm or less than 5 mm.

According to a further embodiment, the single-aperture plate is arrangedat a distance from the aperture which is less than one half, inparticular one fourth, of a focal length which a lens function of theapertures of the multi-aperture plate provides to the beamlets passingtherethrough.

According to still a further embodiment, the single-aperture plate isarranged at such a distance from the multi-aperture plate that anelectric field on a surface of the multi-aperture plate is higher than100 V/mm, higher than 200 V/mm, higher than 300 V/mm, higher than 500V/mm, or higher than 1 kV/mm.

According to another embodiment, a distance between the multi-apertureplate and the first single-aperture plate is less than five times adiameter of the single aperture, less than three times the diameter ofthe single aperture, less than two times this diameter or even less thanthe diameter of the single aperture itself.

For providing a stronger dependency of the beam-manipulating effect ofthe plurality of apertures across the aperture array, it is preferred toprovide a second single-aperture plate arranged in-between themulti-aperture plate and the first single-aperture plate. A thirdvoltage supply is provided for supplying a predetermined third voltageto the second single-aperture plate. The third voltage may be chosensuch that it is substantially equal to or lower than the average of thefirst voltages, or the third voltage may be chosen such that it isin-between the second voltage and the average of the first voltages.

A first single-aperture plate may be provided on both sides of themulti-aperture plate.

According to a further embodiment of the present invention there isprovided a particle-optical arrangement comprising, similar to thearrangements described herein before, at least one charged-particlesource for generating a beam of charged particles, and at least onemulti-aperture plate having a plurality of apertures formed therein.

A first focusing lens is arranged in a beam path of the beam of chargedparticles in-between the charged-particle source and the multi-apertureplate. The first focusing lens has an effect of reducing a divergence ofthe beam of charged particles generated by the source for illuminatingthe plurality of apertures formed in the multi-aperture plate withcharged particles. The charged-particle beam downstream of the firstfocusing lens may be either a divergent beam or a parallel beam.However, a divergence or parallelity of the beam should correspond to adesired divergence or parallelity to a high accuracy.

In practice, lens errors, such as an opening error or a chromatic error,contribute to a deviation from the desired divergence or parallelity.

A decelerating electrode for providing a decelerating electrical fieldin a region between the first focusing lens and the multi-aperture plateis provided for decelerating the charged particles after passing thefirst focusing lens to a desired kinetic energy for passing themulti-aperture plate. Thus, the kinetic energy of the charged particlespassing the focusing field is higher than the desired kinetic energy ofthe charged particles passing the multi-aperture plate.

A possible advantage of such arrangement is a reduced contribution to achromatic error of the first focusing lens at increased kineticenergies.

The inventors have found that a focusing effect of a multi-apertureplate having a plurality of apertures formed therein may be wellcontrolled and relatively accurately adjusted even when a kinetic energyof the electrons penetrating the multi-aperture plate is high. This mayreduce chromatic aberration of a charged-particle beamlet traversing arespective aperture.

Thus, according to a further embodiment of the invention, a kineticenergy of the electrons impinging on or traversing the multi-apertureplate may be higher than 5 keV, higher than 10 keV, higher than 20 keVor even higher than 30 keV.

According to a further embodiment, the invention provides aparticle-optical arrangement comprising, similar to the arrangementsdescribed hereinabove, at least one charged-particle source, at leastone multi-aperture plate, and a first focusing lens providing a focusingfield in a region upstream and/or downstream of the multi-apertureplate. The particle-optical arrangement further comprises an energychanging electrode for changing a kinetic energy of charged particles ofthe beam in a second region upstream and/or downstream of themulti-aperture plate. In view of reducing errors induced by the firstfocusing lens, the first region where the focusing field is provided andthe second region where the energy changing field is provided areoverlapping regions.

According to an embodiment, the energy changing field is a deceleratingelectrical field for reducing the kinetic energy of the chargedparticles of the beam, and the overlapping regions are locatedsubstantially upstream of the multi-aperture plate.

According to a further embodiment, the energy changing field is anaccelerating field for increasing the kinetic energy of the chargedparticles of the beam, and the overlapping regions are locatedsubstantially downstream of the multi-aperture plate.

An overlap between the energy changing field and the focusing field inthe overlapping regions may be more than 1%, more than 5%, or more than10%.

The overlap between the energy changing field and the focusing field maybe determined by plotting both a field strength of the focusing fieldand a field strength of the energy changing field along a beam axis asrespective curves in arbitrary units and normalized such that peakvalues of both curves are at a same level. An overlapping area underboth curves divided by the total area below one or the other curve maythen be taken as a measure for the overlap.

According to a further embodiment of the invention, there is provided aparticle-optical arrangement comprising, similar to the arrangementdescribed herein above, at least one charged-particle source, at leastone multi-aperture plate, and a first focusing lens providing a focusingfield in a region between the charged-particle source and themulti-aperture plate.

The first focusing lens is provided for reducing a divergence of thecharged-particle beam generated by the source upstream of themulti-aperture plate such that the beam immediately upstream of themulti-aperture plate has a remaining divergence. In other words, a crosssection of the beam when passing the first focusing lens is smaller thana cross section of the beam when impinging on the multi-aperture plate.

With such arrangement it is possible to illuminate apertures of amulti-aperture plate with a beam of a given cross section wherein thecross section of the beam passing the first focusing lens is smallerthan the given cross section. This may have an advantage in that anopening error of the first focusing lens may be reduced as compared to afocusing lens collimating the beam for illuminating the given crosssection to form a substantially parallel beam. According to someembodiments, a divergence of the beam immediately upstream of themulti-aperture plate may be higher than 0.5 mrad, higher than 1.0 mrador even higher than 2 mrad, 5 mrad, or 10 mrad.

It should be noted, however, that, according to some embodiments, aconvergent illumination of the multi-aperture plate is advantageous.Applications for such convergent illuminations may be, in particular, inthe field of electron lithography. In practice, a distance betweenadjacent centers of the apertures formed in the multi-aperture plate isa limited distance which may not be further reduced. If suchmulti-aperture plate is illuminated with a parallel beam, also adistance of adjacent foci of the beamlets downstream of themulti-aperture plate will correspond to the distance between adjacentapertures in the multi-aperture plate. By illuminating themulti-aperture plate with a convergent beam it is, however, possible toreduce the distance between adjacent foci of the beamlet whilemaintaining the distance between adjacent apertures of themulti-aperture plate at a same. This allows to form a beam spot patternin an object plane of the apparatus such that the beam spots have verylow distances from each other, that they may contact each other or thatthey even overlap with each other.

Also a convergence of the illuminating beam may be in a range of higherthan 0.5 mrad, higher than 1 mrad or even higher than 2 mrad.

According to a further embodiment of the invention, there is provided aparticle-optical arrangement comprising, similar to the arrangementdescribed herein before, at least one charged-particle source forgenerating a beam of charged particles, at least one multi-apertureplate having a plurality of apertures formed therein, and a firstfocusing lens providing a focusing field portion in a region between thecharged-particle source and the multi-aperture plate. The first focusinglens provides a magnetic field, and the charged-particle source isarranged within the magnetic field provided by the first focusing lens.With such arrangement with the charged-particle source being immersed inthe magnetic field a lens error provided by the focusing field portionmay be reduced.

According to a preferred embodiment, the magnetic field portion in whichthe charged-particle source is provided is a portion with asubstantially homogeneous magnetic field.

According to a further embodiment of the invention, there is provided aparticle-optical arrangement comprising, similar to the arrangementsillustrated herein before, at least one charged-particle source forgenerating a beam of charged particles, and at least one multi-apertureplate having a plurality of apertures formed therein, wherein aplurality of charged-particle beamlets is formed downstream of the atleast one multi-aperture plate such that the respective charged-particlebeamlets each form a focus in a focus region of the multi-aperture platedownstream thereof.

A second focusing lens provides a focusing field in the focus regionwherein the focusing field has a focusing effect on the bundle ofcharged-particle beamlets. The second focusing lens may be necessary atsome position downstream of the multi-aperture plate for some designreason according to which the particle-optical arrangement is designed.The position of the focusing field region of the second focusing fieldsuch that it coincides with the focus region of the multi-aperture platemay have an advantage in that an angular error of a respective beamletat its focus, such as a chromatic error at the focus, has a reducedeffect on the beamlet in a region downstream of the second focusing lenswhere an image of the focusing region is formed.

According to a further embodiment of the invention, there is provided aparticle-optical arrangement comprising, similar to the arrangementsillustrated herein before, at least one charged-particle source and atleast one multi-aperture plate for focusing charged-particle beamlets toeach have a focus in a focusing region of the multi-aperture platedownstream thereto.

An objective lens is provided for imaging the focusing region or anintermediate image thereof onto an object positionable in an objectplane of the arrangement. By imaging foci of the charged-particlebeamlets onto the object it is possible to obtain beam spots ofcomparatively low diameters on the object.

Further, the apertures in the at least one aperture plate may beprovided with diameters substantially greater than diameters of thebeamlets in a region of the foci. Thus, it is possible to form the smallfoci of the beamlets with comparatively large aperture diameters. Aratio of the total area of the apertures over the total area of theaperture pattern is also comparatively high, accordingly. This ratiodetermines an efficiency of beamlet generation, i.e. a ratio of thetotal electron current of all beamlets over a total current of a beamilluminating the multi-aperture plate. Due to the large diameterapertures formed in the multi-aperture plate such efficiency will becomparatively high.

According to a further embodiment of the invention, there is provided anelectron-optical arrangement providing a function of a beam pathsplitter and beam path combiner, respectively. The arrangement mayprovide a primary beam path for a beam of primary electrons directedfrom a primary electron source to an object which is positionable in anobject plane of the arrangement, and a secondary beam path for secondaryelectrons originating from the object The primary and secondary beampaths may be beam paths for single or plural beams of electrons. Forapplications as illustrated herein above, the primary and secondary beampaths are preferable beam paths for a plurality of electron beamlets,however.

The arrangement comprises a magnet arrangement having first, second andthird magnetic field regions. The first magnetic field region is passedby both the primary and secondary electron beam paths and performs thefunction of separating those from each other. The second magnetic fieldregion is arranged upstream of the first magnetic field region in theprimary electron beam path and is not passed by the secondary electronpath. The third magnetic field region is arranged in the secondaryelectron beam path downstream of the first magnetic field region and isnot passed by the first electron beam path.

The first and second magnetic field regions deflect the primary electronbeam in substantially opposite directions and the first and thirdmagnetic field regions deflect the secondary electron beam path in asubstantially same direction.

The arrangement has a low number of only three necessary magnetic fieldregions but may be still designed such that, for a given kinetic energyof the primary electrons and a given kinetic energy of the secondaryelectrons the arrangement provides electron-optical properties which arein first order stigmatic and/or in first order distortion free.

According to a preferred embodiment, a deflection angle of the secondmagnetic field region for the primary electron beam path is higher thana deflection angle of the first magnetic field region for the primaryelectron beam path. Herein, it is further preferred that an intermediateimage is not formed in the primary electron beam path between the firstand second magnetic field regions.

According to a further preferred embodiment, a first drift region, whichis substantially free of magnetic fields, is provided in the primaryelectron beam path between the second and first magnetic field regions.

According to a further preferred embodiment, a second drift region,which is substantially free of magnetic fields, is provided in thesecondary electron beam path between the first and third magnetic fieldregions. It is, however, also possible, that substantially no seconddrift region is provided in the secondary electron beam path between thefirst and third magnetic field regions. If both the first and seconddrift regions are provided, it is then preferred that the second driftregion is substantially shorter than the first drift region.

According to a further preferred embodiment, a focusing lens is providedin-between of the first magnetic field region and the object plane,wherein the focusing lens is passed by both the primary and secondaryelectron beam paths. In view of an application of an electron microscopethe focusing lens may be embodied as an objective lens.

Herein, it is further preferred that at least one electrode is providedin both the first and second electron beam paths for decelerating theprimary electrons before impinging on the object and for acceleratingthe secondary electrons after emerging from the object. With suchelectrode it is possible to change a kinetic energy with which theprimary electrons impinge on the object while the kinetic energy of theprimary electrons passing the magnet arrangement is maintained at a samevalue. Thus, it is possible to maintain the electron-optical propertiesof the beam path splitter/combiner at substantially sameelectron-optical properties while it is possible to change the kineticenergy of the primary electrons impinging on the object. A high accuracyof focusing the primary electrons on the object is achievable over acomparatively large range of kinetic energies of the primary electronsimpinging on the object, accordingly.

Herein, it is further preferred that the magnet arrangement comprises afourth magnetic field region in the secondary electron beam pathdownstream of the third magnetic field region, wherein a magnetic fieldstrength in the third magnetic field region is adjustable relative to amagnetic field strength in the first magnetic field region. The fieldstrength in the fourth magnetic field region may be adjusted independence of the voltage supplied to the pair of electrodes. Since achange of the voltage supplied to the pair of electrodes changes thekinetic energy of the secondary electrons entering the magnetarrangement, the deflection angle of the first magnetic field region forthe secondary electron beam path will also change. The possibility toadjust the field strength in the third and fourth magnetic field regionsprovides the possibility to compensate for such changes on the secondaryelectron beam path caused by changes of the voltage supply to the pairof electrodes. In fact, the fourth magnetic field region may provide afunction of a compensating deflector.

Further, the change of kinetic energies of the secondary electronsentering the magnet arrangement may result in a change of a quadrupoleeffect on the secondary electron beam path and caused by the first andthird magnetic field regions. Preferably, at least one electron-opticalcomponent for compensating such change in the quadrupole effect is alsoprovided in the secondary electron beam path. Such compensatingcomponent may be provided by one or two additional magnetic fieldregions provided in the secondary electron beam path, or one or twoquadrupole lenses provided in the secondary electron beam path, orcombinations of additional field regions and quadrupole lenses providedin the secondary electron beam path.

According to a preferred embodiment there is provided a fifth magneticfield region in the secondary electron beam path downstream of thefourth magnetic field region, and a quadrupole lens downstream of thefifth magnetic field region. A field strength provided by the quadrupolelens and/or the fifth magnetic field region is preferably adjustable independence of the voltage supplied to the at least one electrode.

According to a further preferred embodiment, an intermediate image ofthe object plane is formed by the secondary electrons in a regioncomprising the first, third, fourth and fifth magnetic field regions.

BRIEF DESCRIPTION OF THE DRAWINGS

The forgoing as well as other advantageous features of the inventionwill be more apparent from the following detailed description ofpreferred embodiments of the invention with reference to theaccompanying drawings.

FIG. 1 schematically illustrates basic features and functions of anelectron microscopy system according to an embodiment of the invention;

FIGS. 2 a–2 d show schematic sections through variants of multi-aperturearrangements which may be used in the electron microscopy systemaccording to FIG. 1;

FIG. 3 is a schematic diagram for illustrating electron-opticalcomponents for illuminating a multi-aperture arrangement and formanipulating beamlets of electrons generated by the multi-aperturearrangement;

FIG. 4 shows an example of a primary electron beamlet generatingarrangement which may be used in the electron microscopy system of FIG.1;

FIG. 5 shows plural physical properties of a beam path provided by thearrangement as shown in FIG. 4;

FIG. 6 shows an example of a primary electron beamlet generatingarrangement which may be used in the electron microscopy system of FIG.1;

FIG. 7 shows an array pattern of apertures formed in a multi-apertureplate;

FIG. 8 is a detailed view of a shape of an aperture having additionalshape features for compensating a multipole effect caused by the patternarrangement of apertures as shown in FIG. 7;

FIG. 9 shows an arrangement of apertures and field correcting aperturesprovided in a multi-aperture plate;

FIG. 10 is a cross section of the plate as shown in FIG. 9 along a lineX—X indicated therein;

FIG. 11 shows a hexagonal array pattern of apertures;

FIG. 12 shows a distorted pattern of primary electron beam spots;

FIG. 13 shows an aperture arrangement for compensating a distortion asshown in FIG. 12;

FIG. 14 shows a primary electron beam spot pattern distorted due to anastigmatism;

FIG. 15 shows a plane view on an aperture pattern for compensating anastigmatism distortion as shown in FIG. 14;

FIG. 16 illustrates an effect of a field curvature caused byelectron-optical components involved in imaging a focus plane onto anobject;

FIG. 17 illustrates a multi-aperture arrangement suitable forcompensating a field curvature as illustrated in FIG. 16;

FIG. 18 shows an elevational view on a multi-aperture pattern forcompensating a field curvature;

FIG. 19 illustrates a further multi-aperture arrangement forcompensating a field curvature;

FIGS. 20 a–20 e illustrate further multi-aperture arrangements forcompensating a field curvature;

FIG. 21 is a schematic illustration of a primary electron beam path;

FIG. 22 schematically illustrates a beam splitter/combiner arrangementin cooperation with an objective arrangement which may be used in theelectron microscopy system as shown in FIG. 1; and

FIG. 23 is an illustration of an electron lithography system accordingto an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the exemplary embodiments described below, components that aresimilar in function and structure are designated as far as possible bysimilar reference numerals. Therefore, to understand the features of theindividual components of a specific embodiment, the descriptions ofother embodiments and of the summary of the invention should be referredto.

FIG. 1 is a schematic diagram symbolically illustrating basic functionsand features of an electron microscopy system 1. The electron microscopysystem 1 is of a scanning electron microscope type (SEM) using aplurality of primary electron beamlets 3 for generating primary electronbeam spots 5 on a surface of an object 7 to be inspected which surfaceis arranged in an object plane 101 of an objective lens 102 of anobjective arrangement 100.

Insert I₁ of FIG. 1 shows an elevational view on object plane 101 with aregular rectangular array 103 of primary electron beam spots 5 formedthereon. In FIG. 1 a number of 25 primary electron beam spots 5 arrangedin a 5×5-array 103 is shown. This number of primary electron beam spotsis a low number for ease of illustrating the principles of the electronmicroscopy system 1. In practice, the number of primary electron beamspots may be chosen substantially higher, such as 30×30, 100×100 orothers.

In the illustrated embodiment the array 103 of primary electron beamspots 5 is a substantially regular rectangular array with asubstantially constant pitch P₁ in a range of 1 μm to 10 μm. It is,however, also possible that the array 103 is a distorted regular arrayor an irregular array or an array of some other symmetry, such as ahexagonal array.

A diameter of the primary electron beam spots formed in the object plane101 may be in a range of 5 nm to 200 nm. The focusing of the primaryelectron beamlets 3 to form the primary electron beam spots 5 isperformed by the objective arrangement 100.

The primary electrons incident on the object 7 at the beam spots 5generate secondary electrons emanating from the surface of object 7. Thesecondary electrons form secondary electron beamlets 9 entering theobjective lens 102.

The electron microscopy system 1 provides a secondary electron beam path11 for supplying the plurality of secondary electron beamlets 9 to adetecting arrangement 200. Detecting arrangement 200 comprises aprojecting lens arrangement 205 for projecting the secondary electronbeamlets 9 onto a surface plane 211 of an electron sensitive detector207 of a detector arrangement 209. The detector 207 can be one or moreselected from a solid state CCD or CMOS, a scintillator arrangement, amicro channel plate, an array of PIN diodes and others.

Insert I₂ of FIG. 2 shows an elevational view on image plane 211 and thesurface of detector 207 where secondary electron beam spots 213 areformed as an array 217. A pitch P₂ of array may be in a range of 10 μmto 200 μm. The detector 207 is a position sensitive detector having aplurality of detecting pixels 215. The pixels 215 are arranged in anarray matching with array 217 formed by the secondary electron beamspots 213 such that each pixel 215 can detect an intensity of thesecondary electron beamlet 9 associated therewith.

The primary electron beamlets 3 are generated by a beamlet generatingarrangement 300 comprising an electron source arrangement 301, acollimating lens 303, a multi-aperture plate arrangement 305 and a fieldlens 307.

The electron source arrangement 301 generates a diverging electron beam309 which is collimated by collimating lens 303 to form a beam 311 forilluminating multi-aperture arrangement 305.

Insert I₃ of FIG. 1 shows an elevational view of multi-aperturearrangement 305. Multi-aperture arrangement comprises a multi-apertureplate 313 having a plurality of apertures 315 formed therein. Centers317 of apertures 315 are arranged in a pattern 319 whichelectron-optically corresponds to pattern 103 of the primary electronbeam spots 5 formed in object plane 101.

A pitch P₃ of array 319 may be in a range of 5 μm to 200 μm. Diameters Dof apertures 315 may be in a range of 0.2×P₃ to 0.5×P₃, a range of0.3×P₃ to 0.6×P₃, a range 0.7×P₃, a range of 0.5×P₃ to 0.7×P₃, a rangeof 0.5×P₃ to 0.6×P₃range of 0.7×P₃ to 0.8×P₃, and/or 0.8×P₃ to 0.9×P₃.

Electrons of illuminating beam 311 passing through apertures 315 formthe primary electron beamlets 3. Electrons of illuminating beam 311impinging on plate 313 are intercepted from a primary electron beam path13 and do not contribute to form the primary electron beamlets 3.

As illustrated so far, it is one function of the multi-aperturearrangement 305 to form the plurality of primary electron beamlets 3from the illuminating beam 311. One further function of themulti-aperture arrangement is to focus each primary electron beamlet 3such that foci 323 are generated in a focus region or focus plane 325.

Insert I₄ of FIG. 1 shows an elevational view of focus plane 325 withfoci 323 arranged in a pattern 327. A pitch P₄ of this pattern may be asame or different from pitch P₃ of pattern 319 of multi-aperture plate313 as will be understood from the following specification. A diameterof foci 323 may be in a range of 10 nm to 1 μm

Field lens 307 and objective lens 102 together perform a function ofimaging focus plane 325 onto object plane 101 to form the array 103 ofprimary electron beam spots 5 of a low diameter on the object 7 forachieving a high resolution of secondary electron images generated bydetecting intensities of the secondary electron beamlets 9 by detectorarrangement 209.

A beam splitter/combiner arrangement 400 is provided in the primaryelectron beam path 313 in-between the beamlet generating arrangement 300and objective arrangement 100 and in the secondary electron beam path 11in-between the objective arrangement 100 and the detecting arrangement200.

FIG. 2 shows cross sections of some of a plurality of possibleembodiments of multi-aperture arrangement 305.

FIG. 2 a shows a multi-aperture arrangement 305 having one singlemulti-aperture plate 313 with plural apertures 315 formed therein. Suchsingle multi-aperture plate 313 may perform both the functions ofgenerating the primary electron beamlets 3 from an illuminating beam 311and of focusing the primary electron beamlets 3 downstream ofmulti-aperture plate 313. A focus length f provided by each aperture 315may be estimated according to the formula

$f = {{- 4}\frac{U}{\Delta\; E}}$wherein

-   U is the kinetic energy of electrons passing multi-aperture plate    313 and-   ΔE represents a difference in electric field strengths provided    upstream and downstream of multi-aperture plate 313.

FIG. 2 b shows a multi-aperture arrangement 305 having fourmulti-aperture plates 313 ₁, 313 ₂, 313 ₃, 313 ₄ arranged spaced apartfrom each other in a direction of the primary electron beam path 13.Each of the multi-aperture plates 313 ₁, . . . , 313 ₄ has a pluralityof apertures 315 formed therein wherein the apertures 315 are centeredwith respect to common central axis 317 extending in a direction of theprimary electron beam path.

Multi-aperture plate 313 ₁ is illuminated by illuminating beam 311, andthe apertures 315 formed therein are of a diameter for selecting andgenerating the primary electron beamlets from the illuminating beam 311.Plate 313 ₁ may be supplied with an electrical voltage substantiallyequal to a potential or kinetic energy of the electrons of theilluminating beam 311.

The apertures 315 formed in each of plates 313 ₂, 313 ₃, 313 ₄ are of anequal diameter larger than the diameter of apertures 315 formed inilluminated plate 313 ₁. Plates 313 ₂ and 313 ₄ are thin plates andplate 313 ₃ has a higher thickness than plates 313 ₂ and 313 ₄. Equalvoltages may be supplied to plates 313 ₂ and 313 ₄, and a voltagedifferent therefrom may be supplied to plate 313 ₃, such that a functionof an Einzel-lens is performed on each primary electron beamlet selectedby illuminated plate 313 ₁.

FIG. 2 c shows a multi-aperture arrangement 305 having an illuminatedmulti-aperture plate 313 ₁ with small diameter apertures 315 forselecting primary electron beamlets formed therein. Two multi-apertureplates 313 ₂ and 313 ₃ having a greater thickness than illuminatedaperture 313 ₁ are provided downstream of illuminated multi-apertureplate 313 ₁ for performing a function of an immersion lens on eachprimary electron beamlet. Different voltages will then be supplied toplates 313 ₂ and 313 ₃ for achieving the focusing function of themulti-aperture arrangement 305 during operation thereof.

FIG. 2 d shows a variant of the immersion lens type multi-aperturearrangement shown in FIG. 2 c. The arrangement shown in FIG. 2 c mayhave a disadvantage in that electrical fields generated along a givenaxis 317 due to the different voltages applied to plates 313 ₂, 313 ₃will be effected by stray fields of corresponding fields generated alongdirectly adjacent or more distant axes 317. These stray fields willusually not have a rotational symmetry about given axis 317 such thatthe function of the round lens provided by the immersion lensarrangement is adversely effected.

The multi-aperture arrangement 305 of FIG. 2 d has an insulating spacer331 sandwiched between multi-aperture plates 313 ₂ and 313 ₃ wherein aconductive layer 333 covers an interior of apertures 315 in insulatingspacer 331.

The conductive layer 315 is sufficiently conductive for performing ascreening function for generating stray fields and for screeningremaining stray fields generated by adjacent apertures.

According to an embodiment, the arrangement 305 of FIG. 2 d may bemanufactured as follows: a plate-shaped silicon substrate is provided asthe insulating spacer 331; a silicon oxide layer is formed on both theupper and lower surfaces of the plate; upper 313 ₂ and lower 313 ₃ metallayers are deposited on the upper and lower silicon oxide layer,respectively; a resist pattern defining the apertures 315 is provided onthe upper metal layer 313 ₂; apertures 315 are formed in the upper metallayer 313 ₂ by metal etching, using a conventional etching agent;corresponding apertures are formed in the upper silicon oxide layer bysilicon oxide etching, using a conventional etching agent; apertures 315are formed in the silicon substrate by silicon etching, using aconventional etching agent; corresponding apertures are formed in thelower silicon oxide layer by silicon oxide etching; apertures 315 areformed in the lower metal layer 313 ₃ by metal etching to finally form athrough-hole through the structure of the silicon substrate and thesilicon oxide and metal layers provided thereon. Subsequently anoxidation process is performed for depositing an oxide layer on thesurfaces of the upper 313 ₂ and lower 313 ₃ metal layers, and fordepositing an oxide layer on the interior wall of the through-hole.Finally, a resistive layer is deposited on the oxide layer deposited onthe interior wall of the through-hole. A sputtering process may be usedfor depositing the resistive layer. The resistive layer is depositedsuch that a resistance between upper 313 ₂ and 313 ₃ metal layer is in arange of 250 Ω to 8 MΩ. A rapid thermal oxidation (RTO) process or anelectrochemical oxidation process may be used for depositing the oxidelayer.

FIG. 3 is a further schematic diagram of an embodiment of beamletgenerating arrangement 300.

As shown in FIG. 3, an electron source arrangement 301 generates ahighly divergent electron beam 309 originating from a virtual source329. In the illustrated embodiment, the electron source is of a thermalfield emission (TFE) type having an angular intensity of 1 to 3 mA/srand an emission half angle of 100 mrad.

A collimating lens 303 is arranged in a beam path of divergent beam 309and has a focusing power such that highly divergent beam 309 istransformed to an illuminating beam 311 of a reduced divergence.Divergent illuminating beam 311 then illuminates an illuminated regionF₁ of a multi-aperture plate 313 of multi-aperture arrangement 305. Theillumination of multi-aperture plate 313 with diverging beam 311 has thefollowing advantages over an illumination of region F₁ with a parallelbeam:

A cross section F₂ traversed by the beam 309, 311 in collimating lens303 is substantially smaller than the illuminated area F₁. A collimatinglens of a reduced diameter may be used as compared to an illuminationwith the parallel beam, thus reducing opening errors introduced bycollimating lens 303. Further, a focusing power of collimating lens 303may be reduced as compared to a focusing lens for transforming divergentbeam 309 to a parallel beam which also contributes to reducing errorsintroduced by collimating lens 303.

Further, a decelerating electric field region 321 indicated by across-hatched area in FIG. 3 is provided upstream of multi-apertureplate 313. The electrons of illuminating beam 311 are decelerated indecelerating field region 317 to a desired kinetic energy designed suchthat foci 323 of the primary electron beamlets 3 are formed in a focusplane 325 downstream of multi-aperture arrangement 305. As a consequencethe primary electrons have a higher kinetic energy when passingcollimating lens 303 such that a chromatic error (ΔE/E) of collimatinglens 303 may also be reduced.

Field lens 307 is arranged such that a location of a focusing effectthereof coincides with focus plane 325 or the focus region where thefoci 323 of the primary electron beamlets 3 are formed by themulti-aperture arrangement 305. This has an advantage that a lens error,such as a chromatic error, of field lens 307 has a reduced effect on theprimary electron beam spots 5 formed on object 7 arranged in objectplane 101. Such chromatic error of field lens 307 will result in anangular error of electron beams starting at foci 323. Since, however,the foci 323 are imaged onto the object 7 such angular errors will haveno effect, and also electron beams starting with an angular error fromfoci 323 will hit the object plane substantially at a correct imageposition corresponding to a position of the respective 323. The angularerror generated by field lens 307 will then only effect a landing angleof the primary electron beamlets 3 at the primary electron beam spots 5formed on the object 7. Positions of the beam spots are not effected bysuch error.

FIG. 4 schematically illustrates a further variant of a structure of aprimary electron beamlet generating arrangement 300. A virtual source319 is arranged on a z-axis in a beam liner tube 339 having a downstreamend flange 340. A multi-aperture plate 313 is mounted in a center of acup-shaped electrode 341. The electrons are extracted from source 319with a voltage of 30 kV and between flange 340 and electrode 341 aretarding field of about 350 V/mm is generated upstream ofmulti-aperture plate 313.

FIG. 5 shows some physical properties of the arrangement 300 of FIG. 4plotted along the z-axis in arbitrary units. A curve 342 indicates thedecelerating electrical field generated between electrodes 340, 341. InFIG. 5 the source 319 is located at z=0 mm and the multi-aperture plateis located at z=270 mm.

The source 319 is immersed in a magnetic field of collimating lens 303.A curve 343 in FIG. 5 shows the magnetic field strength oriented inz-direction and generated by collimating lens 303 in dependence ofthe-position along the z-axis. As can be seen from FIG. 5, the source319 is located in a portion of the field generated by the lens whereB_(z) is substantially constant. Such constant magnetic field has only alow focusing effect and a very low aberration on the electrons emittedfrom the source 319. The main focusing effect is achieved at thoseportions of the magnetic field B_(z) where the same has a substantialgradient. From FIG. 5 it appears that the focusing function ofcollimating lens 303 is provided at z-positions from about 200 mm to 300mm. The focusing power of collimating lens 303 coincides with thedecelerating electrical field 342 generated by electrodes 340, 341. Suchcoinciding focusing magnetic field and decelerating electrical fieldallows to provide a focusing function on the primary electron beam whilemaintaining optical errors introduced therewith at a low level. This isevident from a line 344 shown in FIG. 5 indicating the development of achromatic error C_(s) of the optical arrangement along the z-axis. C_(s)is zero at z=0 and increases with increasing values of z. Due to theoverlapping magnetic and electrical field regions it is possible toreduce C_(s) to a value close to zero at a position 345 at about z=230mm. Downstream of this position 345 C_(s) then continuously increasesagain.

FIG. 6 shows a further variant of a primary electron beamlet generatingarrangement 300 having a electron source 319 immersed in a constantportion of a magnetic field of a collimating lens 303 and within a beamtube 339 having a downstream flange electrode 340. Electrode 340 isopposite to an electrode 341 provided as an upstream flange of a furtherbeam tube 348. A multi-aperture arrangement 305 is provided in beam tube348 close to a downstream end thereof. Between electrodes 340 and 341 adecelerating electrical field is generated which overlaps with afocusing gradient magnetic field generated by collimating lens 303.

At a surface of multi-aperture arrangement a remaining electrical fieldis relatively small.

The multi-aperture arrangement 305 generates a plurality of primaryelectron beamlets (not shown in detail in FIG. 6) each having a focus ina focus plane 325.

FIG. 7 shows a pattern 319 of apertures 315 formed in a multi-apertureplate 313, similar to insert I₃ of FIG. 1. Each non-periperhal aperture“a” has four directly neighboring apertures “b”, “c”, “d” and “e”, andit has four second closest neighboring apertures “f”, “g”, “h” and “i”.FIG. 7 indicates a basic array vector [10] in which apertures 315 arearrayed at the closest neighbor pitch, and FIG. 7 indicates a basicarray vector [11] in which the apertures 315 are arrayed with a secondclosest neighbor pitch. From FIG. 7 it can be seen that stray fieldsgenerated by apertures “b” through “i” adjacent to given aperture “a”have a fourfold symmetry about a center 317 of the given aperture. Thesestray fields will cause a distorting effect on the focusing performanceon the beamlet which passes through given aperture “a”.

FIG. 8 illustrates an embodiment for correcting such multipole strayfields generated by apertures adjacent to given aperture “a”. Aperture“a” has a basic circular shape wherein additional features having afourfold symmetry are arranged about center 317 of given aperture “a”are provided about “a” circumference of aperture “a”. The additionalfeatures are formed as shaped protrusions 351 of the aperture into plate313. Additional features 351 have an influence on stray fields generatedby the apertures provided with the additional features. The additionalfeatures are designed such that, if the same are provided to each ofapertures “a” through i, a multipole component of the stray fieldsgenerated with respect to given aperture “a” are reduced.

The additional features having the same symmetry as the closestneighbors of a given aperture may be provided at an aperture of anybasic shape. For instance, the basic shape may be circular, ellipticalor of some other shape.

FIG. 9 shows a further embodiment of reducing an effect of stray fieldshaving a multipole characteristic. Again, apertures 315 are arranged ina rectangular regular array pattern 319. Apertures 315 (5×5-apertures inthe example of FIG. 9) are involved in manipulating electron beamletspassing therethrough. At interstitial positions between apertures 315smaller field correcting apertures 353 are formed. The field correctingapertures 353 also form a rectangular regular grid of a same pitch asgrid 319. The grid of the field correcting apertures 353 is displacedfrom grid 319 of the apertures by one half of a pitch.

A diameter of the field correcting apertures 353 is determined such thata multipole characteristic of stray fields generated by both theapertures 315 and the field correcting apertures 353 is reduced ascompared to the situation shown in FIG. 7 where no field correctingapertures 353 are provided.

FIG. 10 shows a cross section through the multi-aperture arrangement 305shown in FIG. 9. The multi-aperture arrangement 305 comprises aninsulating spacer 331 sandwiched between two multi-aperture plates 313 ₁and 313 ₂. The apertures 315 are formed as through-holes through all ofthe multi-aperture plates 313 ₁, 313 ₂ and the insulating spacer 331,whereas the field correcting apertures 353 are only formed in the uppermulti-aperture plate 313 ₁ exposed to an illuminating electron beam 311,and in the insulating spacer 331. The multi-aperture plate 313 ₂ doesnot have apertures formed at those positions corresponding to positionsof apertures 353 formed in the upper multi-aperture plate 313 ₁ and inthe insulating spacer 331.

According to an embodiment, the multi-aperture arrangement 305 shown inFIG. 10 may be manufactured by a method such as a lithographic processwherein a substrate, such as a mono-crystalline silicon substrate havinga surface oriented in a (110) lattice plane of the substrate, forminginsulating spacer 331 is provided on both surfaces thereof with ametallization layer forming multi-aperture plates 313 ₁ and 313 ₂,respectively. A resist pattern defining the apertures 315 is provided onmetallization layer 313 ₁, and a first etching step is performed with aconventional first etching agent which etches metal; a second etchingstep is performed with a conventional second etching agent which etchessilicon, and a third etching step is performed with the first etchingagent to form the through-holes of apertures through all of the layers313 ₁, 331 and 313 ₂. Thereafter, the resist pattern corresponding tothe pattern of the field correcting apertures 353 is provided on plate313 ₁ and etching is performed with the first etching agent throughupper layer 313 ₁. Thereafter, etching is continued with the secondetching agent which etches only silicon and does not etch metal. Thus,apertures 353 are formed through silicon substrate 331, and etching isstopped at the bottom of apertures 353 in the silicon substrate; lowermetal layer 313 ₂ has a function of an etch stop, accordingly.

A multi-aperture component as shown in one of FIGS. 2 a, 2 b, 2 c, 2 dand in FIG. 10 may be obtained, for example, from Team Nanotec GmbH,78052 Villingen-Schwenningen, Germany.

Now reference is made to FIG. 7 again.

The central aperture of the aperture array 319 is surrounded by two rowsof further apertures adjacent thereto at upper, lower, left and rightsides. In contrast thereto central peripheral aperture “g” does not haveany adjacent apertures at its right side, and upper peripheral aperture“f” does not have adjacent apertures provided at its upper and rightsides. The surrounding electrical field will be different for centralaperture “h”, central peripheral aperture “g” and upper peripheralaperture “f”. Thus, apertures “h”, “gi” and “f” will have differentbeam-manipulating effects on the respective beamlets passingtherethrough. Such differences will be particularly increased forapertures close to a periphery of pattern 319 of the beam-manipulatingapertures.

FIG. 9 shows one embodiment of the invention that reduces suchinfluences on peripheral beam-manipulating apertures. The array 319(5×5-apertures in the illustrated example) is surrounded by additionalapertures 354. In FIG. 9 one row of additional apertures 354 is formedaround a periphery of array pattern 319. It is, however, possible toprovide two or more rows of additional apertures 354 around theperiphery of array 319. The additional apertures 354 have an effect thatthe peripheral apertures “i”, “b”, “f”, “c”, “g” of the array pattern319 have adjacent apertures on all of the upper, lower, left and rightsides, thus reducing the periphery effect illustrated above.

The additional apertures 354 may be arranged as a continuation ofpattern 319, i.e. they are provided with a same pitch as array 319, andthe additional apertures 354 have the same diameters as those apertures“i”, “b”, “f”, “c”, “g”, . . . located at the periphery of array 319. Itis, however, possible to provide the additional apertures 354 with someother pattern and diameters around the periphery of the pattern 319 ofapertures 315.

The additional apertures 354 may be formed in a similar manner to thefield correcting apertures 353, i.e. not formed as through-holes throughthe multi-aperture arrangement 305 as indicated in FIG. 10. Thus, therewill be no primary electron beamlets emerging from the additionalapertures 354. It is, however, also possible to form the additionalaperture 354 as through-holes through the multi-aperture arrangement 305such that also the additional apertures 354 generate primary electronbeamlets downstream thereof. The beamlets formed by the additionalapertures 354 may then be intercepted by some other means, such as asuitable stop, provided downstream of the multi-aperture arrangement. Itwill be also possible to form the illuminating beam 311 such that onlythe pattern 319 of the apertures 315 is illuminated with theilluminating beam and such that the additional apertures 354 will not beilluminated by the illuminating beam 311.

FIG. 11 shows, similar to FIG. 7, an elevational view on amulti-aperture plate 313 having a plurality of beam-manipulatingapertures 315 formed therein. The apertures 315 are arranged in an array319 which is a regular hexagonal array (like honeycomb). A givenaperture “a” is surrounded by six closest neighboring apertures 315 suchthat stray fields caused by the surrounding apertures at a position ofthe given apertures have a sixfold symmetry. Compared to the rectangulararray of FIG. 7 having a fourfold symmetry, the sixfold symmetry is of ahigher order such that the multipole effect of stray fields generated inthe hexagonal array are substantially reduced when compared to therectangular array.

Reference is now made to FIG. 1 again.

FIG. 1 is a schematic and idealized sketch for illustrating the mainfunctions of the electron microscopy system 1.

Insert I₃ of FIG. 1 shows the apertures 315 of multi-aperturearrangement 305 arranged in a regular rectangular pattern 319 of equalpitch, resulting in primary electron beam spots 5 also arranged in arectangular regular pattern 103 of equal pitch. Patterns 319 and 103electron-optically correspond to each other in that sense that theprimary electron beam path 13 supplies the primary electron beamlets 3generated according to pattern 319 onto the substrate 7 byelectron-optical components to form the pattern 103 on the object. Theelectron-optical components involved therein comprise the electronsource arrangement 301, the collimating lens 303, the multi-aperturearrangement 305, the field lens 307, the beam splitter arrangement 400and the objective arrangement 100. In practice, these electron-opticalcomponents introduce imaging errors such that the rectangular regularpattern will not be transformed into the exactly regular rectangularpattern 103.

FIG. 12 for illustration gives an example of an extremely distortedpattern 103 of primary electron beam spots that will be formed inpractice from the regular rectangular pattern 319 according to theinsert I₃ of FIG. 1. Beam spots 5 will not be arranged in a regularrectangular pattern, and grid lines 107 of pattern 103 will be curvedlines such that a pitch between adjacent beam spots 5 increases with anincreasing distance from a center 109 of pattern 103. Thus, pattern 103has a “lower regularity” or progressively larger aperture displacementerrors, the further each aperture is away from the array center ascompared with pattern 319 of FIG. 1, I₃.

FIG. 13 shows a variant of an array arrangement 319 of apertures 315 ofmulti-aperture plate 313 which may be used to correct a distortion ofthe pattern 103 of beam spots 5 shown in FIG. 12. The apertures 315 ofmulti-aperture plate 313 are positioned along grid lines 357 having acurvature opposite to the curvature of grid lines 107 of pattern 103shown in FIG. 12. Apertures 315 are positioned at a pitch distance fromadjacent apertures. In this example, the pitch distance decreases withincreasing distance from a center 358 of pattern 319.

Pattern 319 is designed such that the primary electron beamletsgenerated thereby result in a rectangular regular pattern 103 of beamspots 5 formed on the object plane, as shown in FIG. 1, I₁.

In an embodiment of the electron microscopy system 1 shown in FIG. 1 itmay be sufficient, however, to improve the regularity of beam spotpattern 103 only to such an extent that pattern 103 has a reduceddistortion or improved regularity, respectively, while it is still notof a perfectly regular rectangular array. For instance, a regularity inonly one direction of the pattern, such as the horizontal direction, orsome other suitable direction may be improved. A regularity in suchdirection may be determined, for instance, by some mathematical methodwell known in the art, such as a Fourier analysis.

FIG. 14 shows a further example (also exaggerated for illustration) of aresulting pattern 103 of beam spots 5 formed on the object plane. Inthis example the electron-optical components involved in forming thepattern 103 introduce a field astigmatism such that the beamlets or beamspots are not formed as small circular spots for each primary electronbeam spot 5 of the pattern 103. Moreover, beam spots 5 are of anelliptical or oval shape with a long axis thereof which increases withincreasing distance from a center 109 of pattern 103.

A desired high resolution of the electron microscopy system 1illustrated in FIG. 1 may not be achieved with distorted beam spots.

FIG. 15 shows a variant of a pattern 319 of apertures 315 of amulti-aperture plate 313 which may be used for compensating such effectof field astigmatism. Apertures 315 are of an elliptical shape having along axis increasing with a distance from a center 358 of pattern 319wherein an orientation of the long axis 1 with respect to center 358 istransverse to the orientation of long axis 1 of beam spots 5 as shown inFIG. 14. With such compensating elliptical or oval shapes it is possibleto reduce an influence of a field astigmatism provided by theelectron-optical components such that an ellipticity of beam spots 5formed on object plane 101 will be reduced.

As illustrated in FIG. 1 it is one feature of the electron microscopysystem 1 that spot plane 325 where foci 323 of the primary electronbeamlets are generated by the multi-aperture arrangement 305 is imagedinto an object plane 101 in which the surface of the object 7 to beinspected is positioned. Preferably, object plane 101 and the surface ofthe object 7 coincide.

In practice, the electron-optical components symbolically illustrated asM in FIG. 16, contribute to a field curvature of the electron-opticalsystem such that flat plane 325 of foci 323 is imaged into a curvedplane 101 close to the object surface 7. It is then not possible thatthe curved object plane 101 coincides with the flat surface of object 7,and the foci 323 are not perfectly imaged onto the surface of object 7,accordingly.

FIG. 17 shows one solution to such problem of field curvature of theoptical components M involved in imaging the focus plane 325 onto objectsurface 7. Multi-aperture arrangement 305 is designed such that theplane 325 where the foci 323 of the primary electron beamlet 3 aregenerated is a curved plane. The curvature of focus plane is chosen suchthat the optical components M image plane 325 into a flat image plane101 such that it is possible to position the object planar surface 7 tocoincide with flat image plane 101.

FIG. 18 shows one variant of a multi-aperture plate 313 of themulti-aperture arrangement 305 for compensating a field curvature bygenerating foci 323 of beamlets 3 on a curved focus plane 325 as shownin FIG. 17. For such purpose a diameter “d” of the apertures 315increases with increasing distance from a center 358 of aperture pattern319. The increase in diameter of the apertures results in a reducedfocusing power of a respective aperture and in an increased focal lengthof the lens function provided by the respective aperture 315. Thus, thefocal length provided by central apertures of pattern 319 are smallerthan focal lengths provided by apertures 315 at the periphery of pattern319, resulting in a curvature of the plane 325 where the foci 323 arelocated as indicated in FIG. 17.

It is to be noted that in the example shown in FIGS. 17 and 18 theeffect of the field curvature is compensated by diameters of theapertures increasing with the distance from the center 358 of pattern319. However, depending on the optical properties of the opticalcomponents M involved in imaging focus plane 325 into object plane 101it may be advantageous to have the aperture diameters “d” decreasingwith increasing distance from center 358. It may also be advantageousthat with increasing distance from the center 358 the diameters increaseto a predetermined distance from the center and decrease thereafter.Further, it is not necessary that the diameters change symmetricallywith respect to center 358 of pattern 319. It is also possible thatdiameters change from the left to the right of pattern 319 or from up todown or vice versa or any combinations thereof.

Further, changes in diameters of apertures 315 may be also used toaccount for variations in an electron density in the illuminating beam311. For instance, if illuminating beam 311 is a non-homogeneous beamwith a highest density in its center, the arrangement as shown in FIG.18 will increase a beam strength of peripheral beamlets 3 with respectto central beams such that all primary electron beamlets 3 may have asubstantially same beam strengths or beam current.

FIG. 19 is a further variant of a multi-aperture arrangement 305 whichmay be used for providing a curved focus plane 325 as indicated in FIG.17. A multi-aperture plate 313 is divided into a central circular plateportion 362 ₀ and a plurality of concentric ring-shaped or annular plateportions 362 ₁, 362 ₂, . . . Adjacent plate portions 362 areelectrically insulated from each other, and in each plate portion 362 aplurality of apertures 315 is formed. A voltage supply 361 is providedfor supplying pre-defined voltages U₀, U₁, U₂, . . . to the respectiveplate portions 362 ₀, 362 ₁, 362 ₂, . . . According to an embodiment,the voltage supply 361 comprises a constant current source 363 and aplurality of resistors R₁, R₂, R₃ . . . and a fixed voltage point 364such that voltages U₀, U₁, U₂ differ from each other. Constant current Iand resistors R₁, R₂, . . . are chosen such that a focal length of thelens function provided by the respective apertures 315 increases withincreasing distance from a center 358 of aperture pattern 319. Accordingto an alternative embodiment, separate voltage sources may be providedfor supplying voltages U₀, U₁, U₂, . . . to the plate portions 362 ₁,362 ₂, . . .

The ring-shaped plate portions 362 ₁, 362 ₂, . . . are electricallyinsulated from each other by an insulating gap 365 indicated in insert Iof FIG. 19. The insulating gap 365 extends in a zigzag line betweenadjacent apertures 315.

It is to be noted that the above-mentioned features of shapes anddesigns of apertures of the multi-aperture plate may be combined witheach other. For instance, an aperture may be of an elliptical shape asshown in FIG. 15 and may comprise additional shape features as shown inFIG. 8. Further, the array arrangement of the apertures may haveaperture positions chosen such that a higher regularity spot pattern isformed on the wafer while the respective apertures in such array are ofelliptical shape or have changing aperture diameters, as shown in FIG.18, and have additional shape features as shown in FIG. 8. Amulti-aperture plate having properties as illustrated above may bemanufactured by a MEMS technology known to the person skilled in theart. Such technology may involve reactive ion etching. Themulti-aperture plate according to one embodiment of the invention may beobtained, for example, from Team Nanotec GmbH, 78052Villingen-Schwenningen, Germany.

FIGS. 20 a to 20 e show further variants of multi-aperture arrangement305 for providing foci of electron beamlets 3 located on a curved focusplane 325.

The multi-aperture arrangement 305 shown in FIG. 20 a comprises amulti-aperture plate 313 having a plurality of apertures 305 formedtherein for generating electron beamlets 3 and focusing the same at foci323 located at a focus plane 325 which is a curved plane. A focal lengthf of an aperture 305 may be calculated by

$f = {{- 4}\frac{U}{\Delta\; E}}$wherein

-   U is the kinetic energy of the electrons of illuminating beam 311    when passing multi-aperture plate 313, and-   ΔE may be written as E₁–E₂ wherein E₁ is an electrical field    strength immediately upstream of multi-aperture plate 313 at a    location of the respective aperture, and E₂ is the electrical field    strength immediately adjacent downstream of the aperture plate 313    at the same location.

Since the kinetic energy U is substantially constant over the crosssection of illuminating beam 311 electrical fields E₁ and E₂ adjacent tothe multi-aperture plate 313 may be shaped such that the focal length fprovided by a respective aperture 315 depends from a position of theaperture across illuminating beam 311. Such shaping of the electricalfields E₁ and E₂ may be achieved by one or plural single-aperture plates367 positioned at a distance upstream or downstream from multi-apertureplate 313. In FIG. 20 a one single-aperture plate 367 is positioned at adistance upstream of multi-aperture plate 313 and an aperture 368 formedin single-aperture plate 367 ₁ is chosen such that illuminating beam 311penetrates aperture 368 to illuminate the apertures 315 formed inmulti-aperture plate 313.

A further single-aperture plate 367 ₂ is positioned at a distancedownstream from multi-aperture plate 313, and a still furthersingle-aperture plate 367 ₃ is positioned at a distance downstream ofsingle-aperture plate 367 ₂. Apertures 368 formed in single-apertureplate 367 ₂, 367 ₃ are designed such that the beamlets 3 generated bymulti-aperture plate 313 may pass the apertures 368.

A voltage supply (not shown in FIG. 20) is provided to supply a voltageof 30 kV in the illustrated example or some other suitable voltage tosingle-aperture plate 367 ₁, a voltage of 9 kV in the illustratedexample or some other suitable voltage to multi-aperture plate 313, avoltage of 9 kV to single-aperture plate 367 ₂ and a voltage of 30 kV tosingle-aperture plate 367 ₃. Field lines of electrical field E₁generated by plates 313 and 367 ₁ upstream of multi-aperture plate 313are indicated in FIG. 20 a as well as field lines of electrical field E₂generated by plates 313, 367 ₂, 367 ₃ downstream of multi-aperture plate313. E₁ is substantially constant across the cross section ofilluminating beam 311 at positions close to multi-aperture plate 313.Electrical field E₂ has a stronger dependence on a lateral position onthe multi-aperture plate 313 as indicated by a field line 369 having acurved shape and penetrating from a space between single-aperture plates367 ₂, 367 ₃ into a space between multi-aperture plate 313 andsingle-aperture plate 367 ₂. An aperture 305 positioned at a center ofthe aperture pattern will have a shorter focal length f than an aperture305 positioned at a periphery of the aperture pattern, resulting in foci323 of beamlet 3 located on a curved focus plane 325 as indicated brokenlines in FIG. 20 a.

FIG. 20 b shows a multi-aperture arrangement 305 of a same structure asthat shown in FIG. 20 a. Different therefrom, single-aperture plate 367₁ is supplied with a same voltage of 9 kV as multi-aperture plate 313,such that electrical field E₁ upstream of multi-aperture plate 313 issubstantially zero. Due to the non-homogeneous electrical field E₂downstream of multi-aperture plate 313 the focal length of apertures 315varies as shown in FIG. 20 b such that the focus plane 325 is a curvedplane.

The multi-aperture arrangement 305 shown in FIG. 20 c comprises onemulti-aperture plate 313 and two single-aperture plates 367 ₁ and 367 ₂positioned upstream of multi-aperture plate 313. One single-apertureplate 367 ₃ is provided downstream multi-aperture plate 313.

Voltages of 30 kV are supplied to single-aperture plates 367 ₁ and 367₃, and voltages of 9 kV are supplied to single-aperture plate 367 ₂ andmulti-aperture plate 313. Upstream electric field E₁ is stronglyinhomogeneous at locations close to multi-aperture plate 313 such that afocal length of the respective apertures 315 depends on their lateralposition in the illuminating beam 311, resulting in a focus plane 325suitably curved for correcting a field curvature as illustrated in FIG.17.

The multi-aperture arrangement 305 shown in FIG. 20 d is of a similarstructure than the arrangement shown in FIG. 20 c. In contrast thereto avoltage of 9 kV is supplied to downstream single-aperture 367 ₃ suchthat a substantially vanishing electrical field E₂ is generateddownstream of multi-aperture plate 313. Still, the inhomogeneouselectrical field E₁ provided upstream of multi-aperture plate 313results in the desired variation of the focal lengths of respectiveapertures across the illuminating beam cross section.

In FIGS. 20 a to 20 d the multi-aperture plate 313 is at a lowerpotential (9 kV) as compared to the outer single-aperture plates 367 ₁,367 ₃, respectively (30 kV). This results in a focusing effect of theapertures 315 such that real foci 323 are generated downstream of themulti-aperture plate 313.

In contrast thereto a multi-aperture arrangement 305 shown in FIG. 20 ehas a multi-aperture plate 313 supplied with 30 kV and a single-apertureplate 367 ₁ upstream and a single-aperture plate 367 ₃ downstream ofmulti-aperture plate 313 are supplied with a lower potential of 9 kV.This results in a defocusing effect of apertures 315 formed inmulti-aperture plate 313 such that virtual foci 323 located on a curvedfocus plane 325 upstream of the multi-aperture plate within the beampath of illuminating beam 311 are generated. Even though the foci 323shown in FIG. 20 e are virtual foci, it is still possible to image thesevirtual foci 323 onto the object to be inspected, wherein the curvatureof focus plane 325 is designed such that a field curvature iscompensated for, as illustrated in FIG. 17.

In the above variants shown in FIG. 20 the voltages of 9 kV and 30 kVare merely exemplary voltages, and it is possible to supply the plates313 and 367 with voltages different therefrom. For instance, thesingle-aperture plates 367 ₂ may be supplied with voltages which areeven slightly lower than the voltage which is supplied to multi-apertureplate 313 and which are lower than the high voltages supplied to plates367 ₁, 367 ₃ in FIG. 20 a and FIG. 20 c and supplied to plate 367 ₃ inFIGS. 20 a, 20 b and 20 c.

FIG. 21 is a schematic illustration of the primary electron beam path 13between focus plane 325 and object plane 101 in which object surface 7is positioned, wherein the beam path in the beam splitter is shownunfolded for ease of representation. Downstream of field lens 307coinciding with focus plane 325 primary electron beam path 13 is aconverging beam path having a cross-over in an intermediate plane 111upstream of objective lens 102 and downstream of beam splitter/combinerarrangement 400 wherein the beam path passes an upstream magnetic fieldportion 403 and a downstream magnetic field portion 407 as illustratedbelow.

FIG. 22 is a schematic illustration of beam splitter arrangement 400 andobjective lens 102. The primary electron beam path 13 comprising theplurality of primary electron beamlets enters a first magnetic fieldportion 403 of beam splitter/combiner arrangement 400. In field portion403 there is provided a homogeneous magnetic field deflecting theprimary electron beam path by an angle a to the left. Thereafter theprimary electron beam path 13 passes a drift region 405 which issubstantially free of magnetic fields such that the primary electronbeam path 13 follows a straight line in drift region 405. Thereafter theprimary electron beam path 13 enters a field region 407 in which ahomogeneous magnetic field is provided for deflecting the primaryelectron beam path 13 by an angle β to the right. Thereafter, primaryelectron beam path 13 enters the objective lens 102 for focusing theprimary electron beamlets onto the surface of object 7 positioned inobject plane 101.

The objective lens arrangement 100 comprises a magnetic lens grouphaving a magnetic focusing function and an electrostatic lens group 115having an electrostatic focusing function on the primary electronbeamlets. Further, the electrostatic lens group 115 comprising an upperelectrode 117 and a lower electrode 119 performs a decelerating functionon the primary electrons by an electrical field generated betweenelectrodes 117 and 119 for decelerating the primary electrons beforeimpinging on object surface 7.

A controller 121 is provided for changing the voltage supplied to lowerelectrode 119 such that the kinetic energy with which the primaryelectrons impinge onto the object, the landing energy, may be adjustedin a range of about 0,3 keV to 2,0 keV. The kinetic energy with whichthe primary electrons pass the beam splitter/combiner arrangement 400 isconstant and independent of the landing energy of the primary electronson the object surface and of a value of 30 keV in the present example.

Field portion 403 extends over a length L₁, drift region extends over alength L₂, second field portion 407 extends over a length L₃ and adistance between a lower edge of second field portion 407 and objectplane 101 is L₄ in the present example. L₁ is about 75 mm, L₂ is about90 mm, L₃ is about 60 mm and L₄ is about 80 mm.

A person skilled in the art will be familiar with the technology fordesigning and constructing the beam splitter comprising plural magneticfield regions as illustrated above. Reference may be made to U.S. Pat.No. 6,040,576 or “SMART: A Planned Ultrahigh-ResolutionSpectromicroscope For BESSY II” by R. Fink et al, Journal of ElectronSpectroscopy and Related Phenomena 84, 1987, pages 231 to 250 or “A BeamSeparator With Small Aberrations” by H. Müller et al, Journal ofElectron Microscopy 48(3), 1999, pages 191 to 204.

The absolute values of the field strength in field portions 403 and 407are about equal, and length L₁ and L₃ of field portions 403 and 407 arechosen such that a spatial dispersion induced by the deflection by theangle α to the left and the subsequent deflection by the angle β to theright is substantially zero. Further, the field portions 403 and 407 andthe drift region 405 are chosen such that the deflections induced by thebeam splitter/combiner arrangement 400 on the primary electron beam path13 are in first order substantially stigmatic and in first ordersubstantially distortion free. Thus, the pattern 327 of the foci 323generated by multi-aperture arrangement 305 may be imaged onto theobject plane 101 with a high quality. This imaging quality is maintainedsubstantially independent of the landing energy of the primary electronsonto the object 7.

The secondary electron beam path 11 comprising the plurality ofsecondary electron beamlets 9 is separated from the primary electronbeam path 13 by field region 407 which deflects the secondary electronbeam path 11 by an angle γ to the right.

The secondary electrons emanating from the object 7 with a kineticenergy range of about 0 eV to 100 eV will be accelerated by theelectrical field generated by upper and lower electrodes 117, 119 to akinetic energy which is dependent on a setting provided by controller121 for adjusting the landing energy of the primary electrons. Thus, thekinetic energy of the secondary electrons entering field region 407 willchange in dependence of the landing energy of the primary electrons.

Instead of using the upper and lower electrodes 117, 119 for generatingthe electrical field, it is also possible to omit lower electrode 119and to use object 7 as lower electrode for generating a major portion ofthe electrical field. A corresponding voltage is then applied to theobject.

Deflection angle γ for the secondary electron beam path 11 provided byfield region 407 will change, accordingly. After leaving field region407, the secondary electron beam path passes a drift region 409 which issubstantially free of magnetic fields before entering a further magneticfield region 411 providing a homogeneous magnetic field deflecting thesecondary electron beam path 11 further to the right. A field strengthof field region 411 may be adjusted by a controller 413. When leavingthe field region 411 the secondary electron beam path 11 immediatelyenters a further field region 415 providing a homogeneous magneticfield, a field strength of which may be also adjusted by controller 413.Controller 413 operates in dependence of a setting of the landing energyof primary electron beams and adjusts the magnetic field strength infield regions 411 and 415 such that the primary electron beam pathleaves field region 415 at a pre-defined position and in a pre-defineddirection which are independent of the landing energy of the primaryelectrons and the deflection angle γ, respectively. Thus, the two fieldregions 411, 415 perform a function of two subsequent beam deflectorswhich make it possible to adjust the secondary electron beam to coincidewith the pre-defined secondary electron beam path 11 when the sameleaves magnetic field region 415.

The changes in the magnetic field strengths of field regions 411, 415caused by controller 413 result in changes of a quadrupole effect whichthese electron optical elements 411, 415 have on the secondaryelectrons. To compensate for such changes of a quadrupole effect afurther magnetic field region 419 is provided immediately downstream offield region 415. In magnetic field region 419 a homogeneous magneticfield is provided, a field strength of which is controlled by controller413. Further, downstream of magnetic field region 419 a quadrupole lens421 is provided which is controlled by controller 413 to compensate incooperation with magnetic field region 419 the remaining quadrupoleeffect induced by field portions 411,415 when compensating the beam pathfor different landing energies of the primary electrons.

The electron-optical components 407, 409, 411, 415, 419 and 421 providedin the secondary electron beam path are configured such that, for oneparticular setting of the landing energy of the primary electrons, thesecondary electron beam path 11 through the beam splitter/combinerarrangement 400 is in first order substantially stigmatic, in firstorder distortion free, and in first order dispersion corrected. Forother settings of the landing energy than 2 kV this imaging quality maybe maintained, a reduction of the dispersion correction to a limitedamount occurs, however.

It is to be noted that an intermediate image of object plane 101 isformed in a region of field portions 407, 411, 415 and 419. A positionof the intermediate image will change along the beam axis in dependenceof the setting of the landing energy of the primary electrons and thekinetic energy of the secondary electrons, accordingly.

It is to be noted that apart from magnetic field regions 403 and 407 nofurther beam deflecting magnetic field regions are provided in theprimary electron beam path 13 of the electron microscopy system 1. Theterm “further beam deflecting magnetic field regions” shall comprisemagnetic field regions which are provided for providing a substantialdeflection angle to the primary electron beam and shall not comprisesuch field regions which are merely present for some other purposes,such as providing a possibility of a fine-adjustment of the primaryelectron beam path. Thus, a beam deflecting magnetic field regionproviding a substantial angle of deflection will be a field regionproviding a deflection angle higher than 5° or higher than 10°. Asalready mentioned such further beam deflecting magnetic field regionsare not present in the primary electron beam path, and still the beamsplitter 400 is configured such that it provides sufficiently welldetermined optical properties for the plurality of primary electronbeamlets passing therethrough such that the high quality primaryelectron beam spot pattern 103 is formed in the object plane. Inparticular, the primary electron beam path is to first order stigmaticand free of distortion.

An electron lithography apparatus will be illustrated with reference toFIG. 23.

The electron lithography system shown in FIG. 23 comprises a beamletgenerating arrangement 300 and an objective arrangement 100. The beamletgenerating arrangement 300 generates a plurality of writing electronbeamlets 3 which are directed to an object 7 by the objectivearrangement 100. The object, such as a semiconductor wafer, is coatedwith a charged-particle-sensitive resist which is exposed by the writingelectron beamlets 3. After developing the resist, and subsequent etchingstructures may be formed in the substrate in dependence on the exposureby the writing beamlets 3.

The writing beamlets are generated in the beamlet generating arrangement300 similar to the generation of primary electron beamlets asillustrated with respect to the electron microscopy system above: Anelectron source arrangement 301 generates a diverging electron beam 309which is collimated by a collimating lens 303 to form a beam 311 forilluminating a multi-aperture arrangement 305. Downstream of themulti-aperture arrangement 305 an array of foci 323 of the writingelectron beamlets is formed.

In a plane 325 where the foci 323 are formed there is provided a beamblanking arrangement 340 for switching the plurality of writing beamsselectively on and off. The beam blanking arrangement 340 comprises afurther multi-aperture plate (not shown in FIG. 23) arranged such that arespective focus 323 is formed in each aperture thereof. Each apertureprovides the function of a beam deflector which may be formed by twoelectrodes on opposite sides of the aperture. The electrodes aresupplied by voltages controlled by a computer. When no voltage isapplied to the electrodes of the aperture, the beamlet passingtherethrough will pass along a straight line, i.e. the beamlet will notbe deflected. When a suitable voltage is supplied to the electrodes anelectrical field will be generated within the aperture to deflect therespective beamlet by a suitable angle.

According to an embodiment the beam blanking arrangement 340 is of atype illustrated in “A Multi-Blanker For Parallel Electron BeamLithography” by G. I. Winograd, Ph.D. Thesis, Stanford University, 2001,which document is incorporated herein by reference.

Downstream of plane 325 where the foci 323 are formed there is provideda further multi-aperture plate (not shown in FIG. 23) having a pluralityof apertures positioned such that each writing electron beamlet willpass through the aperture when it is not deflected by the deflectingarrangement, and such that it will substantially not pass through theaperture when the beam is deflected.

Thus, downstream of this further aperture plate the writing electronbeamlets are selectively switched on and off, depending on whether therespective deflector is supplied with a voltage or not. In a situationshown in FIG. 23 only one writing beam passes the beam blanking unit,i.e. only one beam is switched on.

Downstream of the beam blanking unit there are provided subsequent beamdeflectors 451, 452 for displacing the writing beamlets by a distance dwith respect to their beam path before traversing the beam deflectors451, 452.

The objective arrangement 100 includes an objective lens 102 of a typereferred to as a “comb lens” as it is disclosed in US 2003/0066961 A1.

The objective lens 102 comprises two rows 113 of field source membersextending in a direction transversely to the primary electron beam path.The field source members 115 which may be excited such that a desiredelectrical field configuration is provided at a desired position in aspace between the two rows of field source members. Thus, an accuratebeam-manipulating field configured to focus the plurality of primaryelectron beamlets onto the object may be provided in that region wherethe displaced writing beamlets 3 are incident on the objective lensarrangement 100. By using the comb lens as the objective lens 102 it ispossible to displace the focusing lens function together with a scandeflection provided by the beam deflectors 451, 452, and finely focusedwriting electron beam spots will be formed on the substrate surface.

By switching the respective writing electron beamlets on and off andscanning the writing electron beam spots 5 across the substrate surfaceit is possible to expose the resist provided on the object according toa predefined exposure pattern stored in the controlling computer.

Thus, it will be seen that the disclosure of the present application inparticular includes the following items (1) to (106):

(1) A particle-optical arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles;

at least one multi-aperture plate arranged in a beam path of the atleast one beam of charged particles, wherein the at least onemulti-aperture plate has a plurality of apertures formed therein in apredetermined first array pattern, wherein a plurality ofcharged-particle beamlets is formed from the at least one beam ofcharged particles downstream of the multi-aperture plate, and wherein aplurality of beam spots is formed in an image plane of theparticle-optical apparatus by the plurality of charged-particlebeamlets, the plurality of beam spots being arranged in a second arraypattern; and

at least one particle-optical element for manipulating the at least onebeam of charged particles and/or the plurality of charged-particlebeamlets;

wherein the first array pattern has at least one first patternregularity in a first direction, and the second array pattern has atleast one second pattern regularity in a second directionelectron-optically corresponding to the first direction, and wherein thesecond regularity is higher than the first regularity.

(2) The particle-optical arrangement according to Item (1), wherein thefirst pattern regularity of the first array pattern is reduced withrespect to the second pattern regularity of the second array pattern forcompensating a distortion of the at least one particle-optical element.

(3) The particle-optical arrangement according to Item (2), wherein theat least one particle-optical element comprises an objective lens forfocusing the beamlets onto an object positionable in the image plane.

(4) The particle-optical arrangement according to one of Item (1) to(3), wherein a distance between apertures adjacent to each other in thefirst direction of the multi-aperture plate continuously decreases independence of a distance from a center of the first array pattern.

(5) The particle-optical arrangement according to one of Items (1) to(4), wherein the second array pattern has the second pattern regularityhigher than the first pattern regularity only in one single firstdirection.

(6) The particle-optical arrangement according to Item (5), wherein thesecond pattern is a substantially constant pitch pattern in the onesingle first direction.

(7) The particle-optical arrangement according to one of Items (1) to(6), wherein the second array pattern has the second pattern regularityhigher than the first pattern regularity in two first directionsoriented transversely to each other.

(8) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (7),the arrangement comprising:

at least one charged-particle source for generating at least on beam ofcharged particles;

at least one multi-aperture plate arranged in a beam path of the atleast one beam of charged particles, wherein the at least onemulti-aperture plate has a plurality of apertures formed therein in apredetermined first array pattern, wherein a plurality ofcharged-particle beamlets is formed from the at least one beam ofcharged particles downstream of the multi-aperture plate, and wherein aplurality of beam spots is formed in an image plane of theparticle-optical arrangement by the plurality of charged-particlebeamlets; and

at least one particle-optical element for manipulating the at least onebeam of charged particles and/or the plurality of charged-particlebeamlets;

wherein a diameter of the apertures in the multi-aperture plate varieswith an increasing distance from a center of the first pattern.

(9) The particle-optical arrangement according to Item (8), wherein thediameter of the apertures in the aperture plate increases or decreaseswith the increasing distance from the center of the first pattern forcompensating a field curvature of the at least one particle-opticalelement

(10) The particle-optical arrangement according to Item (8) or (9),wherein the diameter of the apertures in the aperture plate increaseswith the increasing distance from the center of the first pattern forcompensating an inhomogeneous current thereof of the at least one beamof charged particles across a cross section.

(11) The particle-optical arrangement according to one of Item (8) or(10), wherein the diameter of the apertures in the aperture plateincreases with the increasing distance from the center of the firstpattern.

(12) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (11),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles;

at least one multi-aperture plate arranged in a beam path of the atleast one beam of charged particles, wherein the at least onemulti-aperture plate has a plurality of apertures formed therein in apredetermined first array pattern, wherein a plurality ofcharged-particle beamlets is formed from the at least one beam ofcharged particles downstream of the multi-aperture plate, and wherein aplurality of beam spots is formed in an image plane of theparticle-optical arrangement by the plurality of charged-particlebeamlets; and

at least one particle-optical element for manipulating the at least onebeam of charged particles and/or the plurality of charged-particlebeamlets;

wherein a shape of at least one group of the apertures is an ellipticalshape.

(13) The particle-optical arrangement according to Item (12), whereinthe shape of the at least one group of the apertures is of theelliptical shape for compensating an astigmatism of the at least onefocusing lens.

(14) The particle-optical arrangement according to Item (11) or (13),wherein an ellipticity of the elliptical shape of the aperturesincreases in dependence of a distance of the aperture from a center ofthe first pattern.

(15) The particle-optical arrangement according to one of Items (12) to(14), wherein a long axis of the elliptical shapes of the apertures isradially oriented with respect to a center of the first pattern.

(16) The particle-optical arrangement according to one of Items (12) to(15), wherein a long axis of the elliptical shapes of the apertures isoriented under an angle with respect to a radial direction with respectto a center of the first pattern.

(17) The particle-optical arrangement according to Item (16), whereinthe angle increases in dependence of a distance of the respectiveaperture from the center of the first pattern.

(18) The particle-optical arrangement according to one of Items (1) to(17), further comprising at least one voltage source for supplying atleast one voltage to the at least one multi-aperture plate.

(19) A particle-optical component comprising:

at least one multi-aperture plate having a plurality of apertures formedtherein, each for manipulating particles of a charged particle beamletpassing therethrough;

wherein the multi-aperture plate comprises plural conductive layerportions arranged substantially in a single plane, wherein pluralapertures are formed in each of the plural conductive layer portions,and wherein a resistant gap, in particular a non-conductive gap, isformed between adjacent conductive layer portions.

(20) The particle-optical component according to Item (19), wherein thecomponent is configured such that adjacent conductive layer portions areat different electric potentials.

(21) The particle-optical component according to one of Items (19) to(20), further comprising at least one voltage source for supplyingpredetermined voltages to the plural conductive layer portions.

(22) The particle-optical component according to one of Items (19) to(21), further comprising at least one resistor electrically couplingdifferent conductive layer portions.

(23) The particle-optical component according to Item (22), wherein aresistance of a first resistor connecting a first pair of adjacentconductive layer portions located at a first distance from a center of afirst pattern of the plurality of apertures formed in the at least onemulti-aperture plate is higher than a resistance of a second resistorconnecting a second pair of adjacent conductive layer portions locatedat a second distance smaller than the first distance from the center ofthe first pattern.

(24) The particle-optical component according to one of Items (19) to(23), wherein the plurality of conductive layer portions comprises afirst conductive layer portion substantially surrounding a secondconductive layer portion.

(25) The particle-optical component according to one of Items (19) to(24), wherein the plurality of conductive layer portions comprises aplurality of ring-shaped portions symmetrically arranged with respect toa center of the first pattern.

(26) The particle-optical component according to Item (25), wherein aradial width of the ring-shaped conductive layer portions decreases withan increasing distance from the center of the first pattern.

(27) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (18),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles, or a plurality of charged particle beamlets; and

at least one particle-optical component according to one of Items (19)to (26).

(28) The particle-optical arrangement according to Item (27), wherein aplurality of charged-particle beamlets is formed from the at least onebeam of charged particles downstream of the multi-aperture plate, andwherein a plurality of beam spots is formed in an object plane of theparticle-optical arrangement by the plurality of charged-particlebeamlets;

the arrangement further comprising at least one focusing lens arrangedin a beam path of the at least one beam of charged particles upstream ofthe multi-aperture plate and/or in a beam path of the plurality ofcharged-particle beamlets downstream of the multi-aperture plate;

wherein the arrangement is configured such that adjacent conductivelayer portions are at different electric potentials for compensating afield curvature of the at least one focusing lens.

(29) The particle-optical arrangement according to one of Items (27) to(28), wherein a focusing effect performed by the apertures on arespective beamlet decreases with increasing distance from a center ofthe first pattern.

(30) A particle-optical component, in particular according to one ofItems (19) to (26), the component comprising:

a first multi-aperture plate made of an insulating substrate having aplurality of apertures formed therethrough, wherein at least an interiorof the apertures formed in the insulating substrate is covered with aconductive layer.

(31) The particle-optical component according to Item (30), wherein theconductive layer is further formed on at least one main flat surface ofthe first multi-aperture plate.

(32) The particle-optical component according to Item (30) or (31),wherein at least one second multi-aperture plate is provided on a mainflat surface of the first multi-aperture plate, wherein the aperturesformed in the first multi-aperture plates and apertures formed in thesecond multi-aperture plates form common throughholes through thestructure of the first and second multi-aperture plates.

(33) The particle-optical component according to Item (32), wherein aconductivity of the conductive layer is lower than a conductivity of thesecond multi-aperture plate.

(34) The particle-optical component according to one of Items (30) to(33), wherein an electrical resistance between both main flat surfacesof the first multi-aperture plate is in a range of about 250 Ω to 8 MΩ,a range of about 250 Ω to 4 MΩ, a range of about 4 MΩ to 8 MΩ, a rangeof about 250 Ω to 800 Ω, a range of about 800 Ω to 1.5 MΩ, a range ofabout 1.5 MΩ to 3 MΩ, a range of about 3 MΩ to 5 MΩ, and/or a range ofabout 5 MΩ to 8 MΩ.

(35) A particle-optical component, in particular according to one ofItems (19) to (34), the component comprising:

a first multi-aperture plate having first and second main flat surfacesand a plurality of apertures formed therethrough,

wherein the multi-aperture plate is made of a material having aconductivity such that an electrical resistance between both main flatsurfaces of the first multi-aperture plate is in a range of about 250 Ωto 8 MΩ, a range of about 250 Ω to 4 MΩ, a range of about 4 MΩ to 8 Ω, arange of about 250 Ω to 800 Ω, a range of about 800 Ω to 1.5 MΩ, a rangeof about 1.5 MΩ to 3 MΩ, a range of about 3 MΩ to 5 MΩ, and/or a rangeof about 5 MΩ to 8 MΩ.

(36) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (29),the arrangement comprising:

at least one charged-particle source for generating at least on beam ofcharged particles, or a plurality of charged particle beamlets; and

at least one particle-optical component according to one of Items (30)to (35).

(37) A particle-optical component, in particular in combination with theparticle-optical component according to one of Items (19) to (35), thecomponent comprising:

at least one multi-aperture plate having a plurality ofbeam-manipulating apertures formed therein, each for manipulating acharged-particle beamlet passing therethrough, wherein the plurality ofbeam-manipulating apertures is arranged in a predetermined first arraypattern; and

wherein at least one of the beam-manipulating apertures has associatedtherewith plural field-correcting apertures formed in the multi-apertureplate.

(38) The particle-optical component according to Item (37), wherein eachof the field-correcting apertures associated with a respectivebeam-manipulating aperture has a size smaller than a size of therespective beam-manipulating aperture.

(39) The particle-optical component according to Item (37) or (38),wherein the field correcting apertures are formed as through-holesextending through the multi-aperture plate.

(40) The particle-optical component according to Item (37) or (38)wherein the field correcting apertures are formed as blind-holes havinga bottom formed in the multi-aperture plate.

(41) The particle-optical component according to one of Items (37) to(40), wherein the particular one of the at least one beam-manipulatingaperture having the plural field-correcting apertures associatedtherewith has a number of closest neighboring beam-manipulatingapertures spaced apart in a circumferential direction thereabout,wherein at least one of the field-correcting apertures is positioned,when seen in the circumferential direction, in between two adjacentclosest neighboring beam-manipulating apertures which are locatedadjacent to each other in the circumferential direction.

(42) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (36),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles; and

at least one particle-optical component according to one of Items (35)to (37).

(43) The particle-optical arrangement according to Item (42), furthercomprising a multi-aperture stop for forming the plurality ofcharged-particle beamlets from the beam of charged particles such thatthe field-correcting apertures are not exposed to charged particles,wherein the multi-aperture stop is positioned upstream of theparticle-optical component.

(44) The particle-optical arrangement according to Item (42), furthercomprising a multi-aperture stop for intercepting charged particleshaving passed the field-correcting apertures, wherein the multi-aperturestop is positioned downstream of the particle-optical component.

(45) A particle-optical component, in particular in combination with theparticle-optical component according to one of Items (19) to (41), thecomponent comprising:

at least one multi-aperture plate having a plurality ofbeam-manipulating apertures formed therein, each for manipulatingparticles of a charged-particle beamlet passing therethrough, whereinthe plurality of beam-manipulating apertures is arranged in apredetermined first array pattern; and

wherein at least one of the beam-manipulating apertures has a number Nof closest neighboring beam-manipulating apertures spaced apart in acircumferential direction thereabout, and wherein a symmetry of a shapeof the at least one beam-manipulating aperture comprises a N-foldsymmetry.

(46) A particle-optical component, in particular in combination with theparticle-optical component according to one of Items (19) to (41), thecomponent comprising:

at least one multi-aperture plate having a plurality ofbeam-manipulating apertures formed therein, each for manipulatingparticles of a charged-particle beamlet passing therethrough, whereinthe plurality of beam-manipulating apertures is arranged in apredetermined first array pattern; and

wherein at least one of the beam-manipulating apertures has a shapehaving at least one symmetry component corresponding to a symmetry ofthe first array pattern around the at least one beam-manipulatingaperture.

(47) The particle-optical component according to Item (45) or (46),wherein the first array pattern is a substantially rectangular arraypattern and wherein the symmetry comprises a fourfold symmetry.

(48) The particle-optical component according to Item (45) or (46),wherein the first array pattern is a substantially hexagonal arraypattern and wherein the symmetry comprises a sixfold symmetry.

(49) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (40),the arrangement comprising:

at least one charged-particle source for generating at least on beam ofcharged particles, or a plurality of charged-particle beamlets; and

at least one particle-optical component according to one of Items (45)to (48).

(50) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (49),the arrangement comprising:

at least one charged-particle source for generating at least on beam ofcharged particles, or a plurality of charged-particle beamlets; and

at least one multi-aperture plate arranged in a beam path of the atleast one beam of charged particles and the plurality ofcharged-particle beamlets, respectively, wherein the at least onemulti-aperture plate has a plurality of apertures formed therein in apredetermined first array pattern, and wherein a plurality of beam spotsis formed in an object plane of the particle-optical arrangementdownstream of the multi-aperture plate, the plurality of beam spotsbeing arranged in a second array pattern;

wherein a number of the beam spots is less than a number of theapertures formed in the multi-aperture plate.

(51) The particle-optical arrangement according to Item (50), whereinapertures not contributing to forming the beam spots are formed asblind-holes in the multi-aperture plate.

(52) The particle-optical arrangement according to Item (50) or (51),wherein beamlets forming the beam spots pass the apertures of a centralregion of the first array patern, and

wherein the apertures of a peripheral region of the first array patterndo not contribute to forming the beam spots.

(53) The particle-optical arrangement according to one of Items (50) to(52), further comprising a multi-aperture stop for forming the pluralityof charged-particle beamlets from the beam of charged particles suchthat the apertures of the peripheral region are not exposed to chargedparticles, wherein the multi-aperture stop is positioned upstream of theparticle-optical component.

(54) The particle-optical arrangement according to one of Items (50) to(53), further comprising a multi-aperture stop for intercepting chargedparticles having passed the apertures of the peripheral region, whereinthe multi-aperture stop is positioned downstream of the particle-opticalcomponent.

(55) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (54),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures are arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate,

a first voltage supply for supplying predetermined first voltages to theplurality of apertures,

a first single-aperture plate arranged at a distance upstream ordownstream of the multi-aperture plate, the first single-aperture platehaving a single aperture for allowing the beam of charged particles orthe plurality of charged-particle beamlets to pass therethrough; and

a second voltage supply for supplying a predetermined second voltage tothe first single-aperture plate,

wherein the distance between the multi-aperture plate and the firstsingle-aperture plate is less than five times a diameter of the singleaperture of the first single-aperture plate, preferably less than fourthree the diameter, preferably less than two times the diameter andfurther preferred less than the diameter of the single aperture of thefirst single-aperture plate.

(56) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (55),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures are arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate,

a first voltage supply for supplying predetermined first voltages to theplurality of apertures,

a first single-aperture plate arranged at a distance upstream ordownstream of the multi-aperture plate, the first single-aperture platehaving a single aperture for allowing the beam of charged particles orthe plurality of charged-particle beamlets to pass therethrough; and

a second voltage supply for supplying a predetermined second voltage tothe first single-aperture plate,

wherein the distance between the multi-aperture plate and the firstsingle-aperture plate is less than 75 mm, preferably less than 50 mm,further preferred less than 25 mm, further preferred less than 10 mm,and further preferred less than 5 mm.

(57) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (56),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures are arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate,

a first voltage supply for supplying predetermined first voltages to theplurality of apertures,

a first single-aperture plate arranged at a distance upstream ordownstream of the multi-aperture plate, the first single-aperture platehaving a single aperture for allowing the beam of charged particles orthe plurality of charged-particle beamlets to pass therethrough; and

a second voltage supply for supplying a predetermined second voltage tothe first single-aperture plate,

wherein the distance between the multi-aperture plate and the firstsingle-aperture plate is selected such that it is less than one half,and in particular, less than one fourth, of an average focal length ofthe apertures of the multi aperture plate.

(58) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (57),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures are arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate,

a first voltage supply for supplying predetermined first voltages to theplurality of apertures,

a first single-aperture plate arranged at a distance upstream ordownstream of the multi-aperture plate, the first single-aperture platehaving a single aperture for allowing the beam of charged particles orthe plurality of charged-particle beamlets to pass therethrough; and

a second voltage supply for supplying a predetermined second voltage tothe first single-aperture plate,

wherein the distance between the multi-aperture plate and the firstsingle-aperture plate is selected such that an average electrical fieldon a surface of the multi aperture plate at a center thereof is higherthan 100 V/mm, higher than 200 V/mm, higher than 300 V/mm, higher than500 V/mm, or higher than 1 kV/mm.

(59) The particle-optical arrangement according to one of Items (48) to(58), further comprising:

a second single-aperture plate arranged in between the multi-apertureplate and the first single-aperture plate and substantially parallelthereto, and

a third voltage supply for supplying a predetermined third voltage tothe second single-aperture plate,

wherein the third voltage is below or equal to the average of the firstvoltages, or wherein the third voltage is in between the second voltageand the average of the first voltages.

(60) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (59),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures are arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate,

a first voltage supply for supplying predetermined first voltages to theplurality of apertures,

a first single-aperture plate arranged at a distance upstream ordownstream of the multi-aperture plate, the first single-aperture platehaving a single aperture for allowing the beam of charged particles orthe plurality of charged-particle beamlets to pass therethrough; and

a second voltage supply for supplying a-predetermined second voltage tothe first single-aperture plate,

a second single-aperture plate arranged in between the multi-apertureplate and the first single-aperture plate, and

a third voltage supply for supplying a predetermined third voltagedifferent from the predetermined second voltage to the secondsingle-aperture plate,

wherein an arrangement of the multi aperture plate an the first andsecond single-aperture plates and a setting of the first, second andthird voltages is configured to generate an electrical field at asurface of the multi-aperture plate, wherein a change in the voltagesupplied to the first single-aperture plate such that the third voltageis supplied to the first single-aperture plate will result in a changeof a field strength of the electrical field of more than 1%, more than5%, or more than 10%.

(61) The particle-optical arrangement according to one of Items (55) to(60), further comprising:

a third single-aperture plate arranged at a distance from themulti-aperture plate and substantially parallel thereto, wherein themulti-aperture plate is positioned in between of the first and thirdsingle-aperture plates, the third single-aperture plate having a singleaperture for allowing the beam of charged particles or the plurality ofcharged-particle beamlets to pass therethrough; and

a fourth voltage supply for supplying a predetermined fourth voltage tothe third single-aperture plate,

wherein the distance between the multi-aperture plate and the thirdsingle-aperture plate is less than five times a diameter of the singleaperture of the third single-aperture plate, preferably less than fourthree the diameter, preferably less than two times the diameter andfurther preferred less than the diameter of the single aperture of thethird single-aperture plate.

(62) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (61),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures being arranged in afirst pattern, wherein a plurality of charged-particle beamlets isformed from the beam of charged particles downstream of the apertureplate;

a first focusing lens providing a focusing field in a first regionbetween the charged-particle source and the multi-aperture plate; and

a decelerating electrode providing a decelerating field in a secondregion in between of the first focusing lens and the multi-apertureplate, such that a kinetic energy of the charged particles passing thefirst focusing lens is higher than a kinetic energy of the chargedparticles passing the multi-aperture plate.

(63) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (62),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures being arranged in afirst pattern, and wherein a plurality of charged-particle beamlets isformed from the beam of charged particles downstream of the apertureplate;

wherein a kinetic energy of the beam of charged particles immediatelyupstream of the multi aperture plate is higher than 5 keV, in particularhigher than 10 keV, in particular higher than 20 keV, and in particularhigher than 30 keV.

(64) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (63),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures being arranged in afirst pattern, wherein a plurality of charged-particle beamlets isformed from the beam of charged particles downstream of the apertureplate;

a first focusing lens providing a focusing field in a first regionupstream and/or downstream of the multi-aperture plate; and

an energy changing electrode providing an electrical field for changinga kinetic energy of charged particles of the beam in a second regionupstream and/or downstream of the multi-aperture plate, and wherein thefirst region where the focusing field is provided and the second regionwhere the energy changing field is provided are overlapping regions.

(65) The particle-optical arrangement according to Item (64), whereinthe overlapping regions are located substantially upstream of themulti-aperture plate.

(66) The particle-optical arrangement according to Item (64), whereinthe overlapping regions are located substantially downstream of themulti-aperture plate.

(67) The particle-optical arrangement according to one of Items (64) to(66), wherein the energy changing field is a decelerating electricalfield for reducing the kinetic energy of the charged particles of thebeam.

(68) The particle-optical arrangement according to one of Items (64) to(66), wherein the energy changing field is an accelerating electricalfield for increasing the kinetic energy of the charged particles of thebeam.

(69) The particle-optical arrangement according to one of Items (64) to(68), wherein an overlap between the energy changing field and thefocusing field is more than 1%, in particular more than 5%, or more than10%.

(70) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (69),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures being arranged in afirst pattern, wherein a plurality of charged-particle beamlets isformed from the beam of charged particles downstream of the apertureplate; and

a first focusing lens providing a focusing field in a region between thecharged-particle source and the multi-aperture plate;

wherein the beam of charged particles is a divergent or convergent beamin a region immediately upstream of the multi-aperture plate.

(71) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (70),the arrangement comprising:

at least one charged-particle source for generating at least one beam ofcharged particles,

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures is arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the aperture plate; and

a first focusing lens providing a magnetic field having a focusing fieldportion in a region between the charged-particle source and themulti-aperture plate;

wherein the at least one charged-particle source is arranged within themagnetic field provided by the first focusing lens.

(72) The particle-optical arrangement of Item (71), wherein the magneticfield where the at least one charged-particle source is arranged is asubstantially homogeneous magnetic field.

(73) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (72),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles;

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures is arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the multi-aperture plate,each of the charged-particle beamlets having a focus in a focusingregion of the multi-aperture plate; and

a second focusing lens providing a focusing field in the focusingregion.

(74) A particle-optical arrangement, in particular in combination withthe particle-optical arrangement according to one of Items (1) to (73),the arrangement comprising:

at least one charged-particle source for generating a beam of chargedparticles;

at least one multi-aperture plate having a plurality of apertures formedin the plate, wherein the plurality of apertures is arranged in a firstpattern, wherein a plurality of charged-particle beamlets is formed fromthe beam of charged particles downstream of the multi-aperture plate,each of the charged-particle beamlets having a focus in a focusingregion of the multi-aperture plate downstream of the multi-apertureplate; and

an objective lens for imaging substantially the focusing region of themulti-aperture plate onto an object positionable in an object plane ofthe arrangement.

(75) The particle-optical arrangement according to one of Items (1) to(74), wherein two multi-aperture plates are provided on opposite sidesof an insulating spacer, wherein apertures in both the multi-apertureplates and apertures in the insulating spacer together form a pluralityof through-holes.

(76) The particle-optical arrangement according to one of Items (1) to(74), wherein a central multi-aperture plate is sandwiched between twoinsulating spacers and wherein two outer multi-aperture plates are eachprovided on one respective insulating spacer, wherein apertures in thecentral and outer multi-aperture plates and apertures in the insulatingspacers together form a plurality of through-holes.

(77) The particle-optical arrangement according to one of Items (1) to(76), wherein the apertures of the multi-aperture plate are positionedaccording to a substantially rectangular pattern.

(78) The particle-optical arrangement according to one of Items (1) to(76), wherein the apertures of the multi-aperture plate are positionedaccording to a substantially hexagonal pattern.

(79) An electron-optical arrangement, in particular in combination withthe particle optical-arrangement according to claim one of Items (1) to(78), the electron microscopy arrangement providing a primary beam pathfor a beam of primary electrons directed from a primary electron sourceto an object positionable in an object plane of the arrangement, and asecondary beam path for secondary electrons originating from the object,the electron microscopy arrangement comprising a magnet arrangementhaving:

a first magnetic field region passed by the primary electron beam pathand the secondary electron beam path for separating the primary electronbeam path and the secondary electron beam path from each other,

a second magnetic field region arranged in the primary electron beampath upstream of the first magnetic field region, wherein the secondmagnetic field region is not passed by the secondary electron beam path,and wherein the first and second magnetic field regions deflect theprimary electron beam in substantially opposite directions,

a third magnetic field region arranged in the secondary electron beampath downstream of the first magnetic field region, wherein the thirdmagnetic field region is not passed by the first electron beam path, andwherein the first and third magnetic field regions deflect the secondaryelectron beam path in a substantially same direction.

(80) The electron microscopy arrangement according to Item (79), whereinno further magnetic field regions deflecting the primary electron beamby more than 5°, in particular more than 10°, are provided in theprimary electron beam path apart from the first and second magneticfield regions.

(81) The electron microscopy arrangement according to Item (79) or (80),wherein a deflection angle of the second magnetic field region for theprimary electron beam path is higher than a deflection angle of thefirst magnetic field region for the primary electron beam path.

(82) The electron microscopy arrangement according to one of Items (79)to (81), wherein a deflection angle of the first magnetic field regionfor the secondary electron beam path is lower than a deflection angle ofthe second magnetic field region for the primary electron beam path.

(83) The electron microscopy arrangement according to one of Items (79)to (82), wherein a first drift region, which is substantially free ofmagnetic fields, is provided in the primary electron beam path betweenthe second and first magnetic field regions.

(84) The electron microscopy arrangement according to one of Items (79)to (83), wherein a second drift region, which is substantially free ofmagnetic fields, is provided in the secondary electron beam path betweenthe first and third magnetic field regions.

(85) The electron microscopy arrangement according to one of Items (79)to (84), further comprising an objective lens provided in between of thefirst magnetic field region and the object plane, wherein the objectivelens is passed by the primary and secondary electron beam paths.

(86) The electron microscopy arrangement according to one of Items (79)to (85), further comprising at least one electrode provided in betweenof the first magnetic field region and the object plane, wherein the atleast one electrode is passed by the primary electron beam path fordecelerating the primary electrons before impinging on the object,wherein the at least one electrode is passed by the secondary electronbeam path for accelerating the secondary electrons after emerging fromthe object.

(87) The electron microscopy arrangement according to Item (86), furthercomprising a driver for supplying an adjustable voltage to the at leastone electrode.

(88) The electron microscopy arrangement according to Item (87), furthercomprising a controller for changing a magnetic field strength in thethird magnetic field region relative to a magnetic field strength in thefirst magnetic field region in dependence of the voltage supplied to theat least one electrode.

(89) The electron microscopy arrangement according to Item (88), whereinthe magnet arrangement further comprises a fourth magnetic field regionin the secondary electron beam path downstream of the third magneticfield region, wherein a magnetic field strength in the fourth magneticfield region is adjustable relative to a magnetic field strength in thethird magnetic field region.

(90) The electron microscopy arrangement according to Item (89), furthercomprising a controller for changing the field strength in the fourthmagnetic field region relative to the field strength in the thirdmagnetic field region in dependence of the voltage supplied to the atleast one electrode.

(91) The electron microscopy arrangement according to Item (89) or (90),wherein the third and fourth magnetic field regions are arrangedsubstantially directly adjacent to each other in the secondary electronbeam path.

(92) The electron microscopy arrangement according to one of Items (87)to (91), further comprising at least one quadrupole lens arranged in thesecondary electron beam path downstream of the third magnetic fieldregion, in particular downstream of the fourth magnetic field region.

(93) The electron microscopy arrangement according to Item (92), furthercomprising a controller for changing a field strength of the quadrupolelens in dependence of the voltage supplied to the at least oneelectrode.

(94) The electron microscopy arrangement according to one of Items (89)to (93), further comprising a fifth magnetic field region arranged inthe secondary electron beam path in between of the fourth magnetic fieldregion and the quadrupole lens.

(95) The electron microscopy arrangement according to Item (94), furthercomprising a controller for changing the field strength in the fifthmagnetic field region relative to the field strength in the thirdmagnetic field region in dependence of the voltage supplied to the atleast one electrode.

(96) The electron microscopy arrangement according to Item (94) or (95),wherein the fourth and fifth magnetic field regions are arrangedsubstantially directly adjacent to each other in the secondary electronbeam path.

(97) The electron microscopy arrangement according to one of Items (79)to (96), wherein an intermediate image of the object plane is formed bythe secondary electrons in a region comprising the first, third, fourthand fifth magnetic field regions.

(98) The electron microscopy arrangement according to one of Items (79)to (97), further comprising a detector arranged in the secondary beampath downstream of the third magnetic field region.

(99) The electron microscopy arrangement according to one of Items (79)to (98), further comprising a transfer lens arrangement arranged in thesecondary beam path upstream of the detector.

(100) The electron microscopy arrangement according to one of Items (79)to (99), wherein substantially homogeneous magnetic fields are providedin the first and/or second and/or third and/or fourth and/or fifthmagnetic field regions, respectively.

(101) The electron-optical arrangement according to one of Items (1) to(100), further comprising a comb lens arrangement having a line ofplural of field source members, and a controller for energizing thefield source members such that an electron-optical property provided bythe comb lens is displaceable along the line.

(102) An electron microscopy system for inspecting an objectpositionable in an object plane of the arrangement, the electronmicroscopy system comprising:

the particle-optical arrangement according to one of Items (1) to (101)for generating a plurality of primary electron beamlets focused on theobject; and

a detector for detecting secondary electrons originating from theobject.

(103) The electron microscopy system according to Item (102), wherein aplurality of secondary electron beamlets is formed from the secondaryelectrons originating from the object.

(104) The electron microscopy system according to Item (103), wherein anumber of the secondary electron beamlets detected by the detector islower than a number of primary electron beamlets focused on the object.

(105) An electron lithography system for exposing an electron sensitivesubstrate, the electron lithography system comprising:

the particle-optical arrangement according to one of Items (1) to (101)for generating a plurality of writing electron beamlets focused on thesubstrate.

(106) An electron lithography system according to Item (105), furthercomprising a detector for detecting secondary electrons originating fromthe object.

Therefore, while the present invention has been shown and describedherein in what is believed to be the most practical and preferredembodiments, it is recognized that departures can be made therefromwithin the scope of the invention, which is therefore not to be limitedto the details disclosed herein but is to be accorded the full scope ofthe claims so as to embrace any and all equivalent methods andapparatus.

1. An electron-optical arrangement providing a primary electron beampath for a beam of primary electrons directed from a primary electronsource to an object positionable in an object plane of the arrangement,and a secondary electron beam path for secondary electrons originatingfrom the object, the electron microscopy arrangement comprising a magnetarrangement having: a first magnetic field region traversed by theprimary electron beam path and the secondary electron beam path forseparating the primary electron beam path and the secondary electronbeam path from each other, a second magnetic field region arranged inthe primary electron beam path upstream of the first magnetic fieldregion, wherein the second magnetic field region is not traversed by thesecondary electron beam path, and wherein the first and second magneticfield regions deflect the primary electron beam path in substantiallyopposite directions, a third magnetic field region arranged in thesecondary electron beam path downstream of the first magnetic fieldregion, wherein the third magnetic field region is not traversed by thefirst electron beam path, and wherein the first and third magnetic fieldregions deflect the secondary electron beam path in a substantially samedirection.
 2. The electron microscopy arrangement according to claim 1,wherein no further magnetic field regions deflecting the primaryelectron beam path by more than 5° are provided in the primary electronbeam path from other than the first and second magnetic field regions.3. The electron microscopy arrangement according to claim 2, wherein adeflection angle of the second magnetic field region for the primaryelectron beam path is higher than a deflection angle of the firstmagnetic field region for the primary electron beam path.
 4. Theelectron microscopy arrangement according to claim 1, wherein adeflection angle of the first magnetic field region for the secondaryelectron beam path is lower than a deflection angle of the secondmagnetic field region for the primary electron beam path.
 5. Theelectron microscopy arrangement according to claim 1, wherein a firstdrift region, which is substantially free of magnetic fields, isprovided in the primary electron beam path between the second and firstmagnetic field regions.
 6. The electron microscopy arrangement accordingto claim 1, wherein a second drift region, which is substantially freeof magnetic fields, is provided in the secondary electron beam pathbetween the first and third magnetic field regions.
 7. The electronmicroscopy arrangement according to claim 1, further comprising anobjective lens provided between the first magnetic field region and theobject plane, wherein the objective lens is traversed by the primary andsecondary electron beam paths.
 8. The electron microscopy arrangementaccording to claim 1, further comprising at least one electrode providedbetween the first magnetic field region and the object plane, whereinthe at least one electrode is traversed by the primary electron beampath for decelerating the primary electrons before impinging on theobject, wherein the at least one electrode is traversed by the secondaryelectron beam path for accelerating the secondary electrons afteremerging from the object.
 9. The electron microscopy arrangementaccording to claim 8, further comprising a driver for supplying anadjustable voltage to the at least one electrode.
 10. The electronmicroscopy arrangement according to claim 9, further comprising acontroller for changing a magnetic field strength in the third magneticfield region relative to a magnetic field strength in the first magneticfield region in dependence of the voltage supplied to the at least oneelectrode.
 11. The electron microscopy arrangement according to claim10, wherein the magnet arrangement further comprises a fourth magneticfield region in the secondary electron beam path downstream of the thirdmagnetic field region, wherein a magnetic field strength in the fourthmagnetic field region is adjustable relative to a magnetic fieldstrength in the third magnetic field region.
 12. The electron microscopyarrangement according to claim 11, further comprising a controller forchanging the field strength in the fourth magnetic field region relativeto the field strength in the third magnetic field region in dependenceof the voltage supplied to the at least one electrode.
 13. The electronmicroscopy arrangement according to claim 11, wherein the third andfourth magnetic field regions are arranged substantially directlyadjacent to each other in the secondary electron beam path.
 14. Theelectron microscopy arrangement according to claim 9, further comprisingat least one quadrupole lens arranged in the secondary electron beampath downstream of the third magnetic field region.
 15. The electronmicroscopy arrangement according to claim 14, further comprising acontroller for changing a field strength of the quadrupole lens independence of the voltage supplied to the at least one electrode. 16.The electron microscopy arrangement according to claim 11, furthercomprising a fifth magnetic field region arranged in the secondaryelectron beam path between the fourth magnetic field region and thequadrupole lens.
 17. The electron microscopy arrangement according toclaim 16, further comprising a controller for changing the fieldstrength in the fifth magnetic field region relative to the fieldstrength in the third magnetic field region in dependence of the voltagesupplied to the at least one electrode.
 18. The electron microscopyarrangement according to claim 16, wherein the fourth and fifth magneticfield regions are arranged substantially directly adjacent to each otherin the secondary electron beam path.
 19. The electron microscopyarrangement according to claim 16, wherein an intermediate image of theobject plane is formed by the secondary electrons in a region of thebeam path between the first and fifth magnetic field region.
 20. Theelectron microscopy arrangement according to claim 1, further comprisinga detector arranged in the secondary beam path downstream of the thirdmagnetic field region.
 21. The electron microscopy arrangement accordingto claim 20, further comprising a transfer lens arrangement arranged inthe secondary beam path upstream of the detector.
 22. The electronmicroscopy arrangement according to claim 16, wherein substantiallyhomogeneous magnetic fields are provided in at least one of the first,second, third, fourth and fifth magnetic field regions.
 23. Amulti-electron-beamlet inspection system, comprising: a stage formounting an object to be inspected; an electron source arrangement forgenerating an array of primary electron beamlets; an objective lens forfocusing each of the primary electron beamlets on the object, wherein anarray of secondary electron beamlets is generated by the primaryelectron beamlets, the secondary electron beamlets traversing theobjective lens; a beam splitter for separating a secondary electron beampath of the secondary electron beamlets from a primary electron beampath of the primary electron beamlets; a detector arrangement forproducing an array of signals corresponding to the array of secondaryelectron beamlets; wherein the beam splitter includes a magnetarrangement having: a first magnetic field region traversed by theprimary electron beam path and the secondary electron beam path forseparating the primary electron beam path and the secondary electronbeam path from each other, a second magnetic field region arranged inthe primary electron beam path upstream of the first magnetic fieldregion, wherein the second magnetic field region is not traversed by thesecondary electron beam path, and wherein the first and second magneticfield regions deflect the primary electron beam path in substantiallyopposite directions, a third magnetic field region arranged in thesecondary electron beam path downstream of the first magnetic fieldregion, wherein the third magnetic field region is not traversed by thefirst electron beam path, and wherein the first and third magnetic fieldregions deflect the secondary electron beam path in a substantially samedirection.
 24. A method of multi-electron-beamlet inspection of asubstrate, the method comprising: generating an array of primaryelectron beamlets; focusing each primary electron beamlet on thesubstrate such that an array of secondary electron beamlets emanatingfrom the substrate is generated; detecting intensities of the secondaryelectron beamlets; and separating a secondary electron beam path of thesecondary electron beamlets from a primary electron beam path of theprimary electron beamlets using a beam splitter, the beam splitterincluding a magnet arrangement having: a first magnetic field regiontraversed by the primary electron beam path and the secondary electronbeam path for separating the primary electron beam path and thesecondary electron beam path from each other, a second magnetic fieldregion arranged in the primary electron beam path upstream of the firstmagnetic field region, wherein the second magnetic field region is nottraversed by the secondary electron beam path, and wherein the first andsecond magnetic field regions deflect the primary electron beam path insubstantially opposite directions, and a third magnetic field regionarranged in the secondary electron beam path downstream of the firstmagnetic field region, wherein the third magnetic field region is nottraversed by the first electron beam path, and wherein the first andthird magnetic field regions deflect the secondary electron beam path ina substantially same direction.